i386/cpu: Mark CPUID 0x80000008 ECX bits[0:7] & [12:15] as reserved for Intel/Zhaoxin

i386/cpu: Mark CPUID 0x80000008 ECX bits[0:7] & [12:15] as reserved for Intel/Zhaoxin

Per SDM,

80000008H EAX Linear/Physical Address size.
              Bits 07-00: #Physical Address Bits*.
              Bits 15-08: #Linear Address Bits.
              Bits 31-16: Reserved = 0.
          EBX Bits 08-00: Reserved = 0.
              Bit 09: WBNOINVD is available if 1.
              Bits 31-10: Reserved = 0.
          ECX Reserved = 0.
          EDX Reserved = 0.

ECX/EDX in CPUID 0x80000008 leaf are reserved.

Currently, in QEMU, only ECX bits[0:7] and ECX bits[12:15] are encoded,
and both are emulated in QEMU.

Considering that Intel and Zhaoxin are already using the 0x1f leaf to
describe CPU topology, which includes similar information, Intel and
Zhaoxin will not implement ECX bits[0:7] and bits[12:15] of 0x80000008.

Therefore, mark these two fields as reserved and clear them for Intel
and Zhaoxin guests.

Reviewed-by: Tao Su <tao1.su@linux.intel.com>
Tested-by: Yi Lai <yi1.lai@intel.com>
Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
Link: https://lore.kernel.org/r/20250714080859.1960104-3-zhao1.liu@intel.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>