imx-drm: imx-tve: don't call sleeping functions beneath enable_lock spinlock

Enable lock claims that it is serializing tve_enable/disable calls.
However, DRM already serialises mode sets with a mutex, which prevents
encoder/connector functions being called concurrently.  Secondly,
holding a spinlock while calling clk_prepare_enable() is wrong; it
will cause a might_sleep() warning should that debugging be enabled.
So, let's just get rid of the enable_lock.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>