npcx: adc: Add support for npcx7 series ec
npcx: adc: Add support for npcx7 series ec

This CL added the support for additional 5 adc channels on npcx7 series
ec. The pin-mux functionality of adc channels was already introduced in
CL 481561.

BRANCH=none
BUG=none
TEST=No build errors for all boards using npcx5 series.
     Build poppy board and upload FW to platform. No issues found.
     All 10 adc channels passed the test on npcx796f evb.

Change-Id: I2c7458958ff659fce78f265eefa160050dee7daf
Signed-off-by: Mulin Chao <6bbc5af053a1dfdc363be6857f30de4ac3bcbd16@nuvoton.com>
Reviewed-on: https://chromium-review.googlesource.com/497526
Reviewed-by: Randall Spangler <62698fdbb84d1779579ee80c3f39fac22017e5bc@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec