tests: Add MAX78000FTHR test overlay files

Enable the following tests for MAX78000FTHR:

 - tests/drivers/adc/adc_api
 - tests/drivers/counter/counter_basic_api
 - tests/drivers/dma/chan_blen_transfer
 - tests/drivers/dma/loop_transfer
 - tests/drivers/gpio/gpio_basic_api
 - tests/drivers/pwm/pwm_api
 - tests/drivers/spi/spi_loopback
 - tests/drivers/w1/w1_api

Signed-off-by: Yasin Ustuner <Yasin.Ustuner@analog.com>