Blackfin arch: Fix Bug - System with EMAC driver enabled - Core not idling

 - Disable all bits in SIC_IWR unless we are going into a real (DPMC)
   power saving mode. Any Interrupt can wake the core form it's idle state.

 - Remove deep sleep mode as it is not going to be used anywhere:
   We support sleep, sleep deeper and hibernate.

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Bryan Wu <cooloney@kernel.org>