tests: adc: Configure adc_api test for frdm_k82f board

Configures the adc api test to use the arduino header A2 pin on the
frdm_k82f board. This follows frdm_k64f and frdm_kw41z boards, which
also use the arduino header A2 pin for the test.

Signed-off-by: Maureen Helm <maureen.helm@nxp.com>