boards: mec172xmodular_assy6930: Correct EC bootloader settings

Changing the EC ROM bootloader mode to Quad from Dual and
SPI drivestrength to 8mA
This changes are required because of the different SPI flash
used which doesn't support Dual mode.

Signed-off-by: Jose Alberto Meza <jose.a.meza.arellano@intel.com>