x86/alternative: Make debug-alternative selective

Using debug-alternative generates a *LOT* of output, extend it a bit
to select which of the many rewrites it reports on.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20230208171431.253636689@infradead.org