imx: wdog: Skip DTB wdog init on DTB overlay
imx: wdog: Skip DTB wdog init on DTB overlay

When OPTEE is providing a DTB overlay to a subsequent boot stage CFG_DT
will be true as will CFG_EXTERNAL_DTB_OVERLAY.

In this case there will be no DTB for the imx watchdog driver to consume so
do not try to do so.

Signed-off-by: Bryan O'Donoghue <165dc05575478af93ac2f97f67be6e1756010094@linaro.org>
Reviewed-by: Peng Fan <d3c162a96b7fb54e5d94bc77bc2c7cbbce10806f@nxp.com>

pascal-brand-st-dev/optee_os,pascal-brand-st-dev/optee_os,pascal-brand-st-dev/optee_os,pascal-brand-st-dev/optee_os,pascal-brand-st-dev/optee_os