powerpc: Call jump_label_init() in apply_feature_fixups()

Call jump_label_init() early so that we can use static keys for CPU and
MMU feature checks.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>