[AVR32] Fix bogus pte_page() definition

The current definition of pte_page() masks out valid bits from the
physical address, causing vmalloc_to_page() to misbehave. This may
lead to everything from mmap() silently accessing the wrong data to
"invalid pte" errors dumped by the kernel.

Also remove the now-unused definition of PTE_PHYS_MASK.

Thanks to Matteo Vit for discovering this bug.

Signed-off-by: Haavard Skinnemoen <hskinnemoen@atmel.com>