JitArm64: Minor subfzex optimizations

[Sintendo]

Some optimizations that were missed in #13251 for this instruction.

Optimize a == 0 with in-host carry

Before:

0x52800019   mov    w25, #0x0                 ; =0
0x7a1903f9   ngcs   w25, w25
0x1a9f37f5   cset   w21, hs
0x390bd3b5   strb   w21, [x29, #0x2f4]

After:

0x5a9f23f9   csetm  w25, lo

Optimize a == -1 with in-host carry

Before:

0x12800019   mov    w25, #-0x1                ; =-1
0x7a1903fa   ngcs   w26, w25
0x1a9f37f8   cset   w24, hs
0x390bd3b8   strb   w24, [x29, #0x2f4]

After:

0x1a9f37fa   cset   w26, hs