ARM: dts: Fix GPMC Ethernet timings for omap cm-t sbc-t boards for device tree

Looks like we have wrong GPMC timings we have for the cm-t and
sbc-t boards. This can cause occasional strange errors with at
least doing an rsync of large files or doing apt-get dist-upgrade.

Let's fix the issue in two phases. First let's simplify cm-t and
sbc-t to use the shared omap-gpmc-smsc911x.dtsi to avoid fixing
the issue in multiple places. Then we can fix the timings in
a single place with a follow-up patch.

Cc: Dmitry Lifshitz <lifshitz@compulab.co.il>
Signed-off-by: Tony Lindgren <tony@atomide.com>