[RFC PATCH] Support for big page sizes on 44x (Updated)

[Ilya Yanok]

These patches add support for selecting page size on PPC 44x.
First one adds support for 16K/64K pages while second one adds support
for 256K pages along with some hacks.

However there are still number of problems:
1. We can't use default PKMAP_BASE definition with 64KB/256KB pages so
we change it. Not sure that it's optimal. Then redefined PKMAP_BASE is
not aligned on (1<<PMD_SHIFT), don't know if it is really bad.
2. with 16KB/64KB/256KB pages WARN_ON(!pmd_none(*pmd)) is triggered
inside dma_alloc_init() function. Not sure if it is really bad.
3. with 256KB pages ENTRIES_PER_PAGEPAGE in mm/shem.c become zero.
4. We use asm-offsets mechanism to make PTE_SHIFT/PMD_SHIFT available in
assembler but we don't really need the power of asm-offsets here. Maybe
it will be more convinient to just take these defines out of #ifndef
__ASSEMBLY__? But this would change asm-generic...

We would appreciate any comment.

Regards, Ilya.