hugetlb: introduce generic version of huge_ptep_get

hugetlb: introduce generic version of huge_ptep_get

ia64, mips, parisc, powerpc, sh, sparc, x86 architectures use the same
version of huge_ptep_get, so move this generic implementation into
asm-generic/hugetlb.h.

[arnd@arndb.de: fix ARM 3level page tables]
Link: http://lkml.kernel.org/r/20181005161722.904274-1-arnd@arndb.de
Link: http://lkml.kernel.org/r/20180920060358.16606-12-alex@ghiti.fr
Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
Reviewed-by: Luiz Capitulino <lcapitulino@redhat.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Tested-by: Helge Deller <deller@gmx.de>			[parisc]
Acked-by: Catalin Marinas <catalin.marinas@arm.com>	[arm64]
Acked-by: Paul Burton <paul.burton@mips.com>		[MIPS]
Acked-by: Ingo Molnar <mingo@kernel.org>		[x86]
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: David S. Miller <davem@davemloft.net>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James E.J. Bottomley <jejb@parisc-linux.org>
Cc: James Hogan <jhogan@kernel.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Rich Felker <dalias@libc.org>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>