Split core initialization code for EP mode into two, one that doesn't
touch core registers and the other that touches core registers. The latter
would be called/skipped based on the EPC feature 'core_init_notifier'.

In platforms where this is skipped, it would be called indirectly
through hooks from the endpoint function driver.
Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Kishon Vijay Abraham I <kishon@ti.com>