The following commit broke CONFIG_RELOCATABLE support on FSL Book-E
parts:

commit 549e8152
Author: Paul Mackerras <paulus@samba.org>
Date:   Sat Aug 30 11:43:47 2008 +1000

    powerpc: Make the 64-bit kernel as a position-independent executable

The change to __va and __pa to use PAGE_OFFSET & MEMORY_START causes
problems on the Book-E parts because we don't know MEMORY_START until
after we parse the device tree.  We need __va to work properly to even
parse the device tree so we have a chicken an egg.  So go back to using
he other definition of __va/__pa on CONFIG_BOOKE and use the
PAGE_OFFSET/MEMORY_START version on "Classic" PPC64.

Also updated casts to handle phys_addr_t being a different size from
unsigned long (ie 36-bit physical on PPC32).
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>