ARM: OMAP3: Fix errors for omap_l3_smx when booted with device tree

When booting omap3 in device tree mode, we're currently getting
the following errors:

omap_l3_smx omap_l3_smx.0: couldn't request debug irq
omap_l3_smx: probe of omap_l3_smx.0 failed with error -22

This is because we don't have handling in the driver for the
compatible property and instead assume platform data being
passed.

Note that this binding is already documented, and implemented
for the related omap_l3_noc driver for omap4 and later. Looks
like the binding somehow never got never implemented for this
omap_l3_smx driver though.

Let's also remove __exit_p to allow binding and unbinding
of the driver while at it.

Reported-by: Pavel Machek <pavel@ucw.cz>
Reported-by: Russell King <rmk+kernel@arm.linux.org.uk>
Acked-by: Santosh Shilimkar <ssantosh@kernel.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>