x86/coco: Export cc_vendor

commit 3d91c537 upstream.

It will be used in different checks in future changes. Export it directly
and provide accessor functions and stubs so this can be used in general
code when CONFIG_ARCH_HAS_CC_PLATFORM is not set.

No functional changes.

[ tglx: Add accessor functions ]

Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20230318115634.9392-2-bp@alien8.de


Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>