Support more LPC43xx UART configurations
Support more LPC43xx UART configurations

Previously the LPC43xx UART code only supported the pins used for each
UART by the Baminbo210E which is a very small subset of all the pin
configurations actually supported by LPC43xx hardware.

The MRI UART parameters now allow the user to specify the TX and RX
pins separately. Examples:
    MRI_UART_TX_P2_0 MRI_UART_RX_P2_1
    MRI_UART_TX_P6_4 MRI_UART_RX_P6_5

The MRI_UART_0 to MRI_UART_3 specifiers are still supported but they
only work for the pins exposed by the Bambino210E board for each of
those UARTs.

adamgreen/mri,adamgreen/mri,adamgreen/mri