[IA64] Module gp must point to valid memory

Some bits of the kernel assume that gp always points to valid memory,
in particular PHYSICAL_MODE_ENTER() assumes that both gp and sp are
valid virtual addresses with associated physical pages.  The IA64
module loader puts gp well past the end of the module, with no physical
backing.  Offsets on gp are still valid, but physical mode addressing
breaks for modules.  Ensure that gp always falls within the module
body.  Also ensure that gp is 8 byte aligned.

Signed-off-by: Keith Owens <kaos@sgi.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>