py/asmarm: Use builtin func to flush I- and D-cache on ARM 7 archs.

The inline assembler code does not work for __ARM_ARCH == 7.

Signed-off-by: Damien George <damien@micropython.org>

py/asmarm.c

@@ -40,18 +40,18 @@
 
 void asm_arm_end_pass(asm_arm_t *as) {
     if (as->base.pass == MP_ASM_PASS_EMIT) {
-        #if defined(__linux__) && defined(__GNUC__)
+        #if (defined(__linux__) && defined(__GNUC__)) || __ARM_ARCH == 7
         char *start = mp_asm_base_get_code(&as->base);
         char *end = start + mp_asm_base_get_code_size(&as->base);
         __builtin___clear_cache(start, end);
         #elif defined(__arm__)
         // flush I- and D-cache
         asm volatile (
             "0:"
-            "mrc p15, 0, r15, c7, c10, 3\n"
+            "mrc p15, 0, r15, c7, c10, 3\n" // test and clean D-cache
             "bne 0b\n"
             "mov r0, #0\n"
-            "mcr p15, 0, r0, c7, c7, 0\n"
+            "mcr p15, 0, r0, c7, c7, 0\n" // invalidate I-cache and D-cache
             : : : "r0", "cc");
         #endif
     }