Commit 7cf314ba80 made a weak assignment of TF_A_CONFIG in the machine
config file, so that it could be overriden from conf/local.conf with a
straight assignment. However, this variable already has a weak assignment
on include files for the tf-a-stm32mp recipe, which apparently take
precedence over the machine files.
This commit creates a new variable DEY_TF_A_CONFIG in the machine config,
and then uses a straight assignment of TF_A_CONFIG to the new variable on the
tf-a-stm32mp.bbappend.
This allows users to override the machine default and avoids the STM recipe
weak assignment.
Signed-off-by: Hector Palacios <hector.palacios@digi.com>