armjit: Don't reset downcount on fpu instructions.

It's maintained always, oops.
armjit: Fix some downcount issues with rounding.

When setting the rounding mode we need to be super careful about not
destroying flags or R0 if they are needed.
x86jit: Fix some flags/EAX trashing in rounding.

Fixes #6810.
jit: Update rounding mode immediately on ctc1.
Merge pull request #6812 from unknownbrackets/jit-minor

Correctly handle flags/temp regs when setting rounding mode