x86: microcode_amd: modify log messages

Impact: change microcode printk content

Change log level and provide (at least I tried to;-) consistent, short,
meaningful content.

Signed-off-by: Andreas Herrmann <andreas.herrmann3@amd.com>
Cc: Dmitry Adamushko <dmitry.adamushko@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>