parisc: add missing include of asm/page.h to asm/pgtable.h

Fixes these errors:

In file included from arch/parisc/include/asm/io.h:5:0,
                 from include/linux/io.h:22,
                 from include/linux/pci.h:54,
                 from arch/parisc/kernel/setup.c:35:
arch/parisc/include/asm/pgtable.h:92:6: warning: "PAGE_SHIFT" is not defined [-Wundef]
arch/parisc/include/asm/pgtable.h:92:6: warning: "PAGE_SHIFT" is not defined [-Wundef]
arch/parisc/include/asm/pgtable.h:92:6: warning: "BITS_PER_PTE_ENTRY" is not defined [-Wundef]

Signed-off-by: Rolf Eike Beer <eike-kernel@sf-tec.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>