x86/cpu/topology: Define AMD64_CPUID_EXT_FEAT MSR

Add defines for the 0xc001_1005 MSR (Core::X86::Msr::CPUID_ExtFeatures) used
to toggle the extended CPUID features, instead of using literal numbers. Also
define and use the bits necessary for an old TOPOEXT fixup on AMD Family 0x15
processors.

No functional changes intended.

  [ bp: Massage, rename MSR to adhere to the documentation name. ]

Signed-off-by: K Prateek Nayak <kprateek.nayak@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/20250901170418.4314-1-kprateek.nayak@amd.com