x86/fpu: Rework fpu_setup_fpu() uses to split it in two

x86/fpu: Rework fpu_setup_fpu() uses to split it in two

It was trying to do too many things at once and there was no clear way of
defining what it was meant to do. This commit splits the function in two.

  1. A function to return the FPU to power-on reset values.
  2. A x87/SSE state loader (equivalent to the old function when it took
     a data pointer).

The old function also had a concept of "default" values that the FPU
would be configured for in some cases but not others. This patch removes
that 3rd vague initial state and replaces it with power-on reset.

While doing this make sure the abridged control tag is consistent with the
manuals and starts as 0xFF

Signed-off-by: Alejandro Vallejo <alejandro.vallejo@cloud.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>