SPU LLVM: Optimize inline MFC transfers

[Whatcookie]

Tiny optimization, use wider instructions when possible. Likely no noticeable improvement outside of synthetics.

[YuriNator557]

Seems slightly slower than master in the SPU test? Could just be test variance but all 3 tests were slower than master.
spu test pr 12080.txt

[Xcedf]

12900k Slightly better
master:
SPU MFC 64 Bits War completed in 4649 ms (PS3: 3370 ms)
PPU/SPU MFC 64 Bits War completed in 7069 ms (PS3: 4443 ms)
PR:
SPU MFC 64 Bits War completed in 4487 ms (PS3: 3370 ms)
PPU/SPU MFC 64 Bits War completed in 6573 ms (PS3: 4443 ms)

[Darkhost1999]

What CPUs?

Ryzen 5 3600
Master
SPU MFC 64 Bits War completed in 8872 ms (PS3: 3370 ms)
PPU/SPU MFC 64 Bits War completed in 12119 ms (PS3: 4443 ms)
PR
SPU MFC 64 Bits War completed in 9092 ms (PS3: 3370 ms)
PPU/SPU MFC 64 Bits War completed in 12171 ms (PS3: 4443 ms)

[Whatcookie]

I don't think it should have any impact on the 64 bit MFC tests