[lldb][RISCV] Fix float load and stores in RISC-V emulator (#167490)
This patch fixes 2 fundamental problems in emulating `FLW`, `FSW`, `FLD`
and `FSD` instructions.
1. Instructions immediate wasn't sign extended
2. Store instructions always wrote for 64 bits to memory
Also this patch fixes 2 lldb tests for RISC-V: TestThreadJump.py and
TestBreakpointHitCount.py