translate_arm/load_store: Handle unpredictable instructions

This necessated handling literal versions of the instructions separately
as they had different requirements. The rationale for detecting
unpredictable instructions is because:

a. they are unlikely to be outputted by a well-behaved compiler
b. their behaviour may change between different processors

I would rather unpredictable instructions fail loudly than silently do
approximately the right thing.

tests/arm/fuzz_arm.cpp

@@ -643,7 +643,7 @@ TEST_CASE("Fuzz ARM load/store instructions (byte, half-word, word)", "[JitX64]"
             u32 rand = RandInt<u32>(0, 0xFF);
             u32 Rm = RandInt<u32>(0, 14);
 
-            if (W) {
+            if (!P || W) {
                 while (Rn == Rd) {
                     Rn = RandInt<u32>(0, 14);
                     Rd = RandInt<u32>(0, 14);