FifoRecorder: Use std::vector for m_Ram and m_ExRam

No need to delete/recreate the arrays every time a new recording happens. Just zero it out.
FIFO: allocate slightly more for SIMD vertex loader overreads

May fix crashes in rare cases.
Merge pull request #1676 from FioraAeterna/allocatefifo

FIFO: allocate slightly more for SIMD vertex loader overreads
Merge pull request #1670 from lioncash/array

FifoRecorder: Use std::vector for m_Ram and m_ExRam
JIT: support immediate arguments in mulhw
JIT: slightly improved immediate handling in mullw
JIT: optimize stXx

Better handling of immediates, mostly. Use the source address if we can.