x86/mce: Cleanup mce_usable_address()

Move Intel-specific checks into a helper function.

Explicitly use "bool" for return type.

No functional change intended.

Signed-off-by: Yazen Ghannam <yazen.ghannam@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230613141142.36801-4-yazen.ghannam@amd.com