Fix incorrect handling of 64-bit CSR in 32-bit mode: no truncate when updating RegisterFile

[FrBrGeorge]

RARS loops forever when running the following code

        li      a1 3000
        csrr    t2 time
        add     t2 t2 a1
m.loop:
        csrr    t0 time
        # mv    t0 t0
        bgeu    t2 t0 m.loop
        li      a7 10
        ecall

But after uncommenting # mv t0 t0 the code runs as expected (sleeps for 3 seconds).

This happened, I believe, when calling RegisterBlock.updateRegister e. g. here without truncating 64-bit values of a CSR. As the result, t0 keeps value larger than 32-bit MAX_VALUE until any operation is performed on it.

Simplest way is to fix this near the root of the problem — when updating a register block (otherwise we have to check out all the 32/64 API mismatches though the code).