boards: esp_wrover_kit: use gpio hogs for LCD, drop LEDs

Instead of using custom board init code, use a GPIO hog to initialize
the LCD backlight. Note that LCD backlight should be controller by the
display driver, but this is not supported now. Initializing defined LEDs
should be done by the application, using either the GPIO or LEDs driver
classes.

Signed-off-by: Gerard Marull-Paretas <gerard@teslabs.com>