microbit: update of edge connector pin mappings to match updated hardware design.
microbit: update of edge connector pin mappings to match updated hardware design.

Definitions of pins changed as follows:

MICROBIT_PIN_P6 =>  P0_12 (COL9)
MICROBIT_PIN_P7 =>  P0_11 (COL8)
MICROBIT_PIN_P9 =>  P0_10 (COL7)

markshannon/microbit-dal,markshannon/microbit-dal