of/unittest: Rename selftest.c to unittest.c

This is unit testing code. It should use that name because it makes more
sense than 'selftest'. Rename the files to match and rename the config
variable.

Signed-off-by: Grant Likely <grant.likely@linaro.org>

diff --cc drivers/of/Kconfig
Simple merge

diff --cc drivers/of/Makefile
Simple merge

diff --cc drivers/of/unittest-data/testcases.dts
Simple merge

diff --cc drivers/of/unittest-data/tests-interrupts.dtsi
Simple merge

diff --cc drivers/of/unittest-data/tests-match.dtsi
Simple merge

diff --cc drivers/of/unittest-data/tests-phandle.dtsi
Simple merge

diff --cc drivers/of/unittest-data/tests-platform.dtsi
Simple merge

diff --cc drivers/of/unittest.c
Simple merge