x86/cpufeatures: Free up unused feature bits

Linux defined feature bits X86_FEATURE_P3 and X86_FEATURE_P4 are not
used anywhere. Commit f31d731e ("x86: use X86_FEATURE_NOPL in
alternatives") got rid of the last usage in 2008. Remove the related
mappings and code.

Just like all X86_FEATURE bits, the raw bit numbers can be exposed to
userspace via MODULE_DEVICE_TABLE(). There is a very small theoretical
chance of userspace getting confused if these bits got reassigned and
changed logical meaning.  But these bits were never used for a device
table, so it's highly unlikely this will ever happen in practice.

[ dhansen: clarify userspace visibility of these bits ]

Signed-off-by: Sohil Mehta <sohil.mehta@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/all/20241107233000.2742619-1-sohil.mehta%40intel.com