x86/microcode: Simplify init path even more

Get rid of all the IPI-sending functions and their wrappers and use
those which are supposed to be called on each CPU.

Thus:

- microcode_init_cpu() gets called on each CPU on init, applying any new
  microcode that the driver might've found on the filesystem.

- mc_cpu_starting() simply tries to apply cached microcode as this is
  the cpuhp starting callback which gets called on CPU resume too.

Even if the driver init function is a late initcall, there is no
filesystem by then (not even a hdd driver has been loaded yet) so a new
firmware load attempt cannot simply be done.

It is pointless anyway - for that there's late loading if one really
needs it.

Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Ashok Raj <ashok.raj@intel.com>
Link: https://lore.kernel.org/r/20221028142638.28498-3-bp@alien8.de