samples: drivers: adc: update board overlays for LPADC API change

Update board overlays for boards with LPADC IP present on their SOCs, to
use new LPADC API for channel numbering.

For the RT595 and LPCxpresso55S69 EVKs, additional channels are enabled
to demonstrate the resolution and differential channel features of
the LPADC.

Signed-off-by: Daniel DeGrasse <daniel.degrasse@nxp.com>