[LoongArch] Add intrinsics for MOVFCSR2GR and MOVGR2FCSR instructions

[LoongArch] Add intrinsics for MOVFCSR2GR and MOVGR2FCSR instructions

Instruction formats:
`movgr2fcsr fcsr, rj`
`movfcsr2gr rd, fcsr`
MOVGR2FCSR modifies the value of the software writable field
corresponding to the FCSR (floating-point control and status
register) `fcsr` according to the value of the lower 32 bits of
the GR (general purpose register) `rj`.
MOVFCSR2GR sign extends the 32-bit value of the FCSR `fcsr`
and writes it into the GR `rd`.

Add "i32 @llvm.loongarch.movfcsr2gr(i32)" intrinsic for MOVFCSR2GR
instruction. The argument is FCSR register number. The return value
is the value in the FCSR.
Add "void @llvm.loongarch.movgr2fcsr(i32, i32)" intrinsic for MOVGR2FCSR
instruction. The first argument is the FCSR number, the second argument
is the value in GR.

Reviewed By: SixWeining, xen0n

Differential Revision: https://reviews.llvm.org/D140685