target/hppa: Mask reserved PSW bits in expand_sm_imm

target/hppa: Mask reserved PSW bits in expand_sm_imm

The system mask is a restricted subset of the psw, with only
a couple of reserved bits.  It is better to handle this up
front in the translator than require helper_swap_system_mask
to use cpu_hppa_get_psw and cpu_hppa_put_psw.

Signed-off-by: Helge Deller <deller@gmx.de>
[rth: Handle this in expand_sm_imm not helper_swap_system_mask.]
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>