exit: Add PANIC_ON_RECURSIVE_FAULT Kconfig option

If a recursive fault is detected during do_exit(), tasks are left
to sit and wait in an un-interruptible sleep until the system
reboots (typically manually). Add Kconfig option to change this
behaviour and force a panic.

This is particularly important if a critical system task encounters
a recursive fault (ex. a kworker). Otherwise, the system may be
unusable, but since the scheduler is still running system watchdogs
may continue to be pet.

Change-Id: Ifc26fc79d6066f05a3b2c4d27f78bf4f8d2bd640
Signed-off-by: Matt Wagantall <mattw@codeaurora.org>
[abhimany: convert printk to pr_alert]
Signed-off-by: Abhimanyu Kapur <abhimany@codeaurora.org>