x86/microcode/AMD: Increase microcode PATCH_MAX_SIZE

Future AMD CPUs will have microcode patches that exceed the default 4K
patch size. Raise our limit.

Signed-off-by: John Allen <john.allen@amd.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: stable@vger.kernel.org # v4.14..
Link: https://lkml.kernel.org/r/20200409152931.GA685273@mojo.amd.com