ARM: common: fiq_debugger: add non-fiq debugger support

Add irq-only support to the debugger. This allows the debugger
to always run at irq context. This introduces limitations to
being able to debug certain kinds of issues, but it is still
very useful as a debugging tool.

Change-Id: I1e4223e886cb2d90ef5ed31419bdd5cdd7f904ca
Signed-off-by: Dima Zavin <dima@android.com>