x86/microcode/amd: Cache builtin microcode too

save_microcode_in_initrd_amd() fails to cache builtin microcode and only
scans initrd.

Use find_blobs_in_containers() instead which covers both.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20231010150702.495139089@linutronix.de