x86/cpu: Drop vestigial PBE logic in AMD/Hygon/Centaur/Cyrix

x86/cpu: Drop vestigial PBE logic in AMD/Hygon/Centaur/Cyrix

Besides formatting changes, this logic dates back to Linux 2.4.0-test11 in
November 2000.

Prior to "Massive cleanup of CPU detection and bug handling",
c->x86_capability was a single u32 containing cpuid(1).edx,
cpuid(0x80000001).edx, or a synthesis thereof.  X86_FEATURE_AMD3D was
defined as the top bit this single u32.

After "Massive cleanup of CPU detection and bug handling",
c->x86_capability became an array with AMD's extended feature leaf split
away from Intel's basic feature leaf.

AMD doc #20734-G states that 3DNow is only enumerated in the extended
feature leaf, and that other vendors where using this bit too.  i.e. AMD
never produced a CPU which set bit 31 in the basic leaf, meaning that
there's nothing to clear out in the first place.

This logic looks like it was relevant in the pre-"Massive cleanup" world
but ought to have been dropped when c->x86_capability was properly split.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Pu Wen <puwen@hygon.cn>
Link: https://patch.msgid.link/20251126125147.880275-1-andrew.cooper3@citrix.com