mchp: Add ADC MAX reading value for MEC172x
mchp: Add ADC MAX reading value for MEC172x

Update ADC_READ_MAX for MEC172x, its ADC is 12BIT resolution in default

BRANCH=none
BUG=b:190518298
TEST=Tested on ADL RVP via UART console
> temps
  Ambient             : 300 K = 27 C  34%
  DDR                 : 299 K = 26 C  31%
  Skin                : 301 K = 28 C  37%
  VR                  : 297 K = 24 C  25%

Signed-off-by: martin yan <409cb29bb9001f9bb84010e71644764e5f7609ce@microchip.corp-partner.google.com>
Change-Id: If657d79d989b017fb34df437e28ceed291c9e1d3
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2935558
Reviewed-by: Vijay Hiremath <006c712879a3af08bfdb5c2b8491a8b2d5fd73cd@intel.com>
Reviewed-by: Aseda Aboagye <12c9b286316a940fd31c24070da5ab64cdd4d0e7@chromium.org>

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