x86: x86-64: add arch_float_en-/dis-able() functions

This adds arch_float_enable() and arch_float_disable() to x86-64.
As x86-64 always has FP/SSE enabled, these operations are basically
no-ops. These are added just for the completeness of arch interface.

Fixes #38022

Signed-off-by: Daniel Leung <daniel.leung@intel.com>