target-mips: add missing MSACSR and restore fp_status and hflags

target-mips: add missing MSACSR and restore fp_status and hflags

Save MSACSR state. Also remove fp_status, msa_fp_status, hflags and restore
them in post_load() from the architectural registers.
Float exception flags are not present in vmstate. Information they carry
is used only by softfloat caller who translates them into MIPS FCSR.Cause,
FCSR.Flags and then they are cleared. Therefore there is no need for saving
them in vmstate.

Signed-off-by: Leon Alrae <leon.alrae@imgtec.com>
Reviewed-by: Richard Henderson <rth@twiddle.net>