x86/mm: Centralize PMD flags in sme_encrypt_kernel()

x86/mm: Centralize PMD flags in sme_encrypt_kernel()

In preparation for encrypting more than just the kernel during early
boot processing, centralize the use of the PMD flag settings based
on the type of mapping desired.  When 4KB aligned encryption is added,
this will allow either PTE flags or large page PMD flags to be used
without requiring the caller to adjust.

Tested-by: Gabriel Craciunescu <nix.or.die@gmail.com>
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Reviewed-by: Borislav Petkov <bp@suse.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brijesh Singh <brijesh.singh@amd.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20180110192615.6026.14767.stgit@tlendack-t1.amdoffice.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>