boards: add adc support to the mimxrt1050 board

add adc to board dts file,
update yaml files and documentation,
add adc 1 channel pins 1 and 15 to the pinmux file,
add overlay file to the board adc sample,
add board to the adc test file and

Signed-off-by: Andrei Auchynnikau <ovchinnikov@strim-tech.com>