Fix problems booting large kernels on alphas. The symptom is that the kernel

Fix problems booting large kernels on alphas.   The symptom is that the kernel
loads, prints the copyright, and either hangs or locks solid.  The
PC tends to be in the data segment and the RA is in XentMM

Doug really came up with the fix, I'm just the monkey typing.  Doug says:
	The alpha can only support 64k of globals with $gp pointing at
	base+32k so that the code can use 16bit signed offsets from $gp to
	access it. ....  it is possible to have multiple .got subsections
	and the linker handles this with the relocations for 'ldgp' pseudo
	instructions.  [Without this patch] the code in exception.s has been
	linked  to use a different gp from locore.s (where pal_kgp is set).

Reviewed by: dfr