powerpc: Move initial mfspr LPCR out of __init_LPCR

We want to change what's initially set in the LPCR, so start by taking the move
from LPCR out of the function and into the caller.

Signed-off-by: Matt Evans <matt@ozlabs.org>
Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>