powepc/booke: Separate out E.HV check and ivor setup code.

Move the E.HV check and CPU_FTR_EMB_HV flag manipulation to the cpu setup
code.  Create a separate routine for E.HV ivors setup.

Signed-off-by: Varun Sethi <Varun.Sethi@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>