ARC: Fix PAE40 boot failures due to PTE truncation

So a benign looking cleanup which macro'ized PAGE_SHIFT shifts turned
out to be bad (since it was done non-sensically across the board).

It caused boot failures with PAE40 as forced cast to (unsigned long)
from newly introduced virt_to_pfn() was causing truncatiion of the
(long long) pte/paddr values.

It is OK to use this in accessors dealing with kernel virtual address,
pointers etc, but not for PTE values themelves.

Fixes: cJ2ff5cf2735c ("ARC: mm: Use virt_to_pfn() for addr >> PAGE_SHIFT pattern)
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>