x86/tdx: Exclude shared bit from __PHYSICAL_MASK

In TDX guests, by default memory is protected from host access. If a
guest needs to communicate with the VMM (like the I/O use case), it uses
a single bit in the physical address to communicate the protected/shared
attribute of the given page.

In the x86 ARCH code, __PHYSICAL_MASK macro represents the width of the
physical address in the given architecture. It is used in creating
physical PAGE_MASK for address bits in the kernel. Since in TDX guest,
a single bit is used as metadata, it needs to be excluded from valid
physical address bits to avoid using incorrect addresses bits in the
kernel.

Enable DYNAMIC_PHYSICAL_MASK to support updating the __PHYSICAL_MASK.

Co-developed-by: Kuppuswamy Sathyanarayanan <[email protected]>
Signed-off-by: Kuppuswamy Sathyanarayanan <[email protected]>
Signed-off-by: Kirill A. Shutemov <[email protected]>
Signed-off-by: Dave Hansen <[email protected]>
Reviewed-by: Andi Kleen <[email protected]>
Reviewed-by: Tony Luck <[email protected]>
Reviewed-by: Thomas Gleixner <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

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