mm, x86: fix HIGHMEM64 && PARAVIRT build config for native_pud_clear()

mm, x86: fix HIGHMEM64 && PARAVIRT build config for native_pud_clear()

Looks like I also missed the build config that includes
CONFIG_HIGHMEM64G && CONFIG_PARAVIRT to export the native_pud_clear()
dummy function.

Fixes: a00cc7d9dd93d ("mm, x86: add support for PUD-sized transparent hugepages")
Link: http://lkml.kernel.org/r/148823188084.56076.17451228917824355200.stgit@djiang5-desk3.ch.intel.com
Signed-off-by: Dave Jiang <[email protected]>
Reported-by: Laura Abbott <[email protected]>
Reported-by: Boris Ostrovsky <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>