sh: add AT_HWCAP flag for J-Core cas.l instruction

The J-Core cpu has, as an ISA extension, an atomic compare-and-swap
instruction cas.l which applications need to use (instead the imask or
gusa atomic models, which are fundamentally limited to UP) for
synchronization in order to be compatible with SMP systems. Provide a
hwcap flag so that it's possible to do runtime selection and support
both.
Signed-off-by: NRich Felker <dalias@libc.org>

arch/sh/include/uapi/asm/cpu-features.h

@@ -22,5 +22,6 @@
 #define CPU_HAS_L2_CACHE	0x0080	/* Secondary cache / URAM */
 #define CPU_HAS_OP32		0x0100	/* 32-bit instruction support */
 #define CPU_HAS_PTEAEX		0x0200	/* PTE ASID Extension support */
+#define CPU_HAS_CAS_L		0x0400	/* cas.l atomic compare-and-swap */
 
 #endif /* __ASM_SH_CPU_FEATURES_H */

arch/sh/kernel/cpu/sh2/probe.c

@@ -57,6 +57,8 @@ void __ref cpu_probe(void)
 	boot_cpu_data.dcache.entry_shift	= 5;
 	boot_cpu_data.dcache.linesz		= 32;
 	boot_cpu_data.dcache.flags		= 0;
+
+	boot_cpu_data.flags |= CPU_HAS_CAS_L;
 #else
 	/*
 	 * SH-2 doesn't have separate caches