Board: stm32mp1: Add supply current boot information

Board: stm32mp1: Add supply current boot information

For DK1/DK2 boards, check if power supply provides enough current
to allow the board to boot correctly.
ADC@0 channel 18 and 19 are connected to USB type-C CC1 and CC2
signals. The table below shows the behavior for different range of
CC1 or CC2:

  range       | power supply | red led |          console message
  (Volts)     |   (Amps)     | blinks  |
--------------|--------------|---------|-----------------------------------
[2.10 - 1.23[ |     3        |   NO    |    NO
[1.23 - 0.66[ |     1.5      | 3 times | WARNING 1.5A power supply detected
[0.66 - 0]    |     0.5      | 2 times | WARNING 500mA power supply detected

If detected current is < 3A, red led is kept ON after blinking.

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>