hw/xtensa/xtfpga: implement uImage loading

Provide a simple bootloader code at the reset address that jumps to the
loaded image entry point when it's not equal to the reset address. This
is needed because the old method of setting pc doesn't work due to cpu
reset done after the machine setup.
Signed-off-by: NMax Filippov <jcmvbkbc@gmail.com>

hw/xtensa/xtfpga.c

@@ -237,6 +237,7 @@ static void lx_init(const LxBoardDesc *board, MachineState *machine)
 
     /* Use presence of kernel file name as 'boot from SRAM' switch. */
     if (kernel_filename) {
+        uint32_t entry_point = env->pc;
         size_t bp_size = 3 * get_tag_size(0); /* first/last and memory tags */
         uint32_t tagptr = 0xfe000000 + board->sram_size;
         uint32_t cur_tagptr;
@@ -273,7 +274,29 @@ static void lx_init(const LxBoardDesc *board, MachineState *machine)
         int success = load_elf(kernel_filename, translate_phys_addr, cpu,
                 &elf_entry, &elf_lowaddr, NULL, be, ELF_MACHINE, 0);
         if (success > 0) {
-            env->pc = elf_entry;
+            entry_point = elf_entry;
+        } else {
+            hwaddr ep;
+            int is_linux;
+            success = load_uimage(kernel_filename, &ep, NULL, &is_linux);
+            if (success > 0 && is_linux) {
+                entry_point = ep;
+            } else {
+                error_report("could not load kernel '%s'\n",
+                             kernel_filename);
+                exit(EXIT_FAILURE);
+            }
+        }
+        if (entry_point != env->pc) {
+            static const uint8_t jx_a0[] = {
+#ifdef TARGET_WORDS_BIGENDIAN
+                0x0a, 0, 0,
+#else
+                0xa0, 0, 0,
+#endif
+            };
+            env->regs[0] = entry_point;
+            cpu_physical_memory_write(env->pc, jx_a0, sizeof(jx_a0));
         }
     } else {
         if (flash) {