tcg/ppc: Fix tcg_out_rlw_rc

tcg/ppc: Fix tcg_out_rlw_rc

The TCG IR sequence:

  mov_i32 tmp97,$0xc4240000             dead: 1  pref=0xffffffff
  mov_i32 tmp98,$0x0                    pref=0xffffffff
  rotr_i32 tmp97,tmp97,tmp98            dead: 1 2  pref=0xffffffff

was translated to `slwi r15, r14, 0` instead of `slwi r14, r14, 0`
due to SH field overflow.  SH field is 5 bits, and tcg_out_rlw is called
in some situations with `32-n`, when `n` is 0 it results in an overflow
to RA field.

This commit prevents overflow of that field and adds debug assertions
for the other fields

Acked-by: Ilya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: Dani Szebenyi <szedani@linux.ibm.com>
Message-ID: <20241022133535.69351-2-szedani@linux.ibm.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>