i386/tdx: Don't mask off CPUID_EXT_PDCM

i386/tdx: Don't mask off CPUID_EXT_PDCM

It gets below warning when booting TDX VMs:

  warning: TDX forcibly sets the feature: CPUID[eax=01h].ECX.pdcm [bit 15]

Because CPUID_EXT_PDCM is fixed1 for TDX, and MSR_IA32_PERF_CAPABILITIES is
supported for TDX guest unconditioanlly.

Don't mask off CPUID_EXT_PDCM for TDX.

Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Link: https://lore.kernel.org/r/20250625035710.2770679-1-xiaoyao.li@intel.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>