ARM: tegra: fiq_debugger: add support for irq-mode debugger

On platforms with TZ, fiqs are considered secure and thus cannot
be used easily for debugging. Enable using just the irq mode
debugger

Change-Id: I2feefda47acc43c7b3715c716f586e85c82df3b7
Signed-off-by: Dima Zavin <dima@android.com>