kvm: ppc: Add SPRN_EPR get helper function

kvmppc_set_epr() is already defined in asm/kvm_ppc.h, So
rename and move get_epr helper function to same file.

Signed-off-by: Bharat Bhushan <Bharat.Bhushan@freescale.com>
[agraf: remove duplicate return]
Signed-off-by: Alexander Graf <agraf@suse.de>