x86/mm/encrypt: Simplify sme_pgtable_calc()

x86/mm/encrypt: Simplify sme_pgtable_calc()

sme_pgtable_calc() is unnecessary complex. It can be re-written in a
more stream-lined way.

As a side effect, we would get the code ready to boot-time switching
between paging modes.

Tested-by: Tom Lendacky <[email protected]>
Signed-off-by: Kirill A. Shutemov <[email protected]>
Reviewed-by: Tom Lendacky <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>