arm: mx6: Selectively twiddle pfd's

Testing has shown that just gating/ungating all the pfd clocks
can actually trigger the errata that is trying to be worked around.
Instead we use the debug registers to see if a pfd is not locked and
only twiddle it if necessary.
config: mx6_cubox-i: Clean up the auto boot detection

This patch does a massive cleanup of the default boot scripts.
Adding support for ext4, searching both / and /boot for files
auto-detecting and properly loading dtb files and zImage / uImage
kernel types.

Shout out goes to rmk for autodetectfdt scripting.

Signed-off-by: Jon Nettleton <jon.nettleton@gmail.com>
Signed-off-by: Russell King <rmk@arm.linux.org.uk>