MAINTAINERS: Add Intel TDX entry

Add myself as Intel TDX maintainer.

I drove upstreaming most of TDX code so far and I will continue
working on TDX for foreseeable future.

[ dhansen: * Add myself as a reviewer too
	   * Swap Maintained=>Supported.  I double
	     checked Kirill is still being paid
	   * Add drivers/virt/coco/tdx-guest ]

Suggested-by: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Acked-by: Kai Huang <kai.huang@intel.com>
Link: https://lore.kernel.org/all/20231101233314.2567-1-kirill.shutemov%40linux.intel.com