m68k: Fix redefinition of pgprot_noncached

arch/m68k/include/asm/pgtable_mm.h:148:1: warning: "pgprot_noncached" redefined
In file included from arch/m68k/include/asm/pgtable_mm.h:138,
                 from arch/m68k/include/asm/pgtable.h:4,
                 from include/linux/mm.h:40,
                 from include/linux/pagemap.h:7,
                 from include/linux/blkdev.h:12,
                 from arch/m68k/emu/nfblock.c:17:
include/asm-generic/pgtable.h:133:1: warning: this is the location of the previous definition

pgprot_noncached() should be defined _before_ including asm-generic/pgtable.h

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>