target-mips: use deposit instead of hardcoded version

target-mips: use deposit instead of hardcoded version

Use the deposit op instead of and hardcoded bit field insertion. It
allows the host to emit the corresponding instruction if available.

At the same time remove the (lsb > msb) test. The MIPS64R2 instruction
set manual says "Because of the instruction format, lsb can never be
greater than msb, so there is no UNPREDICATABLE case for this
instruction."

(Bug reported as LP:1071149.)
Cc: Никита Канунников <n.kanunnikov@sbtcom.ru>
Reviewed-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>