Convert driver to use DT_INST macros and remove related board per
instance Kconfig symbol usage.
Also update counter_basic_api test to use DT_INST and remove the
udoo_neo_full_m4.conf as its not longer needed since the per instance
Kconfig sybmols don't exist anymore.
Signed-off-by: Kumar Gala <kumar.gala@linaro.org>