x86/smpboot: Remove confusing quirk usage in INIT delay

Very old multiprocessor systems required a 10 msec delay between
asserting and de-asserting INIT but modern processors do not require
this delay.

Over time the usage of the "quirk" wording while setting the INIT delay
has become misleading. The code comments suggest that modern processors
need to be quirked, which clears the default init_udelay of 10 msec,
while legacy processors don't need the quirk and continue to use the
default init_udelay.

With a lot more modern processors, the wording should be inverted if at
all needed. Instead, simplify the comments and the code by getting rid
of "quirk" usage altogether and clarifying the following:

  - Old legacy processors -> Set the "legacy" 10 msec delay
  - Modern processors     -> Do not set any delay

No functional change.

Signed-off-by: Sohil Mehta <sohil.mehta@intel.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20250219184133.816753-10-sohil.mehta@intel.com