x86/virt/tdx: Make TDX host depend on X86_MCE

A build failure was reported that when INTEL_TDX_HOST is enabled but
X86_MCE is not, the tdx_dump_mce_info() function fails to link:

  ld: vmlinux.o: in function `tdx_dump_mce_info':
  ...: undefined reference to `mce_is_memory_error'
  ...: undefined reference to `mce_usable_address'

The reason is in such configuration, despite there's no caller of
tdx_dump_mce_info() it is still built and there's no implementation for
the two "mce_*()" functions.

Make INTEL_TDX_HOST depend on X86_MCE to fix.

It makes sense to enable MCE support for the TDX host anyway.  Because
the only way that TDX has to report integrity errors is an MCE, and it
is not good to silently ignore such MCE.  The TDX spec also suggests
the host VMM is expected to implement the MCE handler.

Note it also makes sense to make INTEL_TDX_HOST select X86_MCE but this
generates "recursive dependency detected!" error in the Kconfig.

Closes: https://lore.kernel.org/all/20231212214612.GHZXjUpBFa1IwVMTI7@fat_crate.local/T/
Fixes: 70060463cb2b ("x86/mce: Differentiate real hardware #MCs from TDX erratum ones")
Reported-by: Arnd Bergmann <arnd@kernel.org>
Signed-off-by: Kai Huang <kai.huang@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Link: https://lore.kernel.org/all/20231212214612.GHZXjUpBFa1IwVMTI7@fat_crate.local/T/#m1a109c29324b2bbd0b3b1d45c218012cd3a13be6
Link: https://lore.kernel.org/all/20231213222825.286809-1-kai.huang%40intel.com

arch/x86/Kconfig

@@ -1974,6 +1974,7 @@ config INTEL_TDX_HOST
 	select ARCH_KEEP_MEMBLOCK
 	depends on CONTIG_ALLOC
 	depends on !KEXEC_CORE
+	depends on X86_MCE
 	help
 	  Intel Trust Domain Extensions (TDX) protects guest VMs from malicious
 	  host and certain physical attacks.  This option enables necessary TDX