The mul_i32 pattern was loading non-16-bit constants into a register,
when we can get the middle-end to do that for us.  The mul_i64 pattern
was not considering that MULLI takes 64-bit inputs.
Reviewed-by: NAurelien Jarno <aurelien@aurel32.net>
Signed-off-by: NRichard Henderson <rth@twiddle.net>