avr32: convert to asm-generic/memory_model.h

Switch avr32/include/asm/page.h to use the common defintions for
pfn_to_page(), page_to_pfn(), and ARCH_PFN_OFFSET.

Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Cc: Haavard Skinnemoen <hskinnemoen@gmail.com>
Cc: Hans-Christian Egtvedt <egtvedt@samfundet.no>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>