target/mips: Disable R5900 support

Disable R5900 support. There are some outstanding issues related
to ABI support and emulation accuracy, that were not understood
well during review process. Disable to avoid backward compatibility
issues.

Reverts commit ed4f49ba.
Reviewed-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: NAleksandar Markovic <amarkovic@wavecomp.com>

target/mips/translate_init.inc.c

@@ -410,65 +410,6 @@ const mips_def_t mips_defs[] =
         .insn_flags = CPU_MIPS32R5 | ASE_MSA,
         .mmu_type = MMU_TYPE_R4000,
     },
-    {
-        /*
-         * The Toshiba TX System RISC TX79 Core Architecture manual
-         *
-         * https://wiki.qemu.org/File:C790.pdf
-         *
-         * describes the C790 processor that is a follow-up to the R5900.
-         * There are a few notable differences in that the R5900 FPU
-         *
-         * - is not IEEE 754-1985 compliant,
-         * - does not implement double format, and
-         * - its machine code is nonstandard.
-         */
-        .name = "R5900",
-        .CP0_PRid = 0x00002E00,
-        /* No L2 cache, icache size 32k, dcache size 32k, uncached coherency. */
-        .CP0_Config0 = (0x3 << 9) | (0x3 << 6) | (0x2 << CP0C0_K0),
-        .CP0_Status_rw_bitmask = 0xF4C79C1F,
-#ifdef CONFIG_USER_ONLY
-        /*
-         * R5900 hardware traps to the Linux kernel for IEEE 754-1985 and LL/SC
-         * emulation. For user only, QEMU is the kernel, so we emulate the traps
-         * by simply emulating the instructions directly.
-         *
-         * Note: Config1 is only used internally, the R5900 has only Config0.
-         */
-        .CP0_Config1 = (1 << CP0C1_FP) | (47 << CP0C1_MMU),
-        .CP0_LLAddr_rw_bitmask = 0xFFFFFFFF,
-        .CP0_LLAddr_shift = 4,
-        .CP1_fcr0 = (0x38 << FCR0_PRID) | (0x0 << FCR0_REV),
-        .CP1_fcr31 = 0,
-        .CP1_fcr31_rw_bitmask = 0x0183FFFF,
-#else
-        /*
-         * The R5900 COP1 FPU implements single-precision floating-point
-         * operations but is not entirely IEEE 754-1985 compatible. In
-         * particular,
-         *
-         * - NaN (not a number) and +/- infinities are not supported;
-         * - exception mechanisms are not fully supported;
-         * - denormalized numbers are not supported;
-         * - rounding towards nearest and +/- infinities are not supported;
-         * - computed results usually differs in the least significant bit;
-         * - saturations can differ more than the least significant bit.
-         *
-         * Since only rounding towards zero is supported, the two least
-         * significant bits of FCR31 are hardwired to 01.
-         *
-         * FPU emulation is disabled here until it is implemented.
-         *
-         * Note: Config1 is only used internally, the R5900 has only Config0.
-         */
-        .CP0_Config1 = (47 << CP0C1_MMU),
-#endif /* !CONFIG_USER_ONLY */
-        .SEGBITS = 32,
-        .PABITS = 32,
-        .insn_flags = CPU_R5900 | ASE_MMI,
-        .mmu_type = MMU_TYPE_R4000,
-    },
     {
         /* A generic CPU supporting MIPS32 Release 6 ISA.
            FIXME: Support IEEE 754-2008 FP.