ARM uses custom implementation of PMD folding in 2-level page table case.
Generic code expects to see __PAGETABLE_PMD_FOLDED to be defined if PMD is
folded, but ARM doesn't do this.  Let's fix it.

Defining __PAGETABLE_PMD_FOLDED will drop out unused __pmd_alloc().  It
also fixes problems with recently-introduced pmd accounting on ARM without
LPAE.
Signed-off-by: NKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reported-by: NNishanth Menon <nm@ti.com>
Reported-by: NSimon Horman <horms@verge.net.au>
Tested-by: NSimon Horman <horms+renesas@verge.net.au>
Tested-by: NFabio Estevam <festevam@gmail.com>
Tested-by: NFelipe Balbi <balbi@ti.com>
Tested-by: NNishanth Menon <nm@ti.com>
Tested-by: NPeter Ujfalusi <peter.ujfalusi@ti.com>
Tested-by: NKrzysztof Kozlowski <k.kozlowski@samsung.com>
Tested-by: NGeert Uytterhoeven <geert+renesas@glider.be>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Russell King <linux@arm.linux.org.uk>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>