gpio: Add Multi-Function-Pin configuration driver for Marvell SoCs

gpio: Add Multi-Function-Pin configuration driver for Marvell SoCs

Most of the Marvell SoCs has Multi Function Pin (MFP) configuration registers
For ex. ARMADA100.

These registers are programmed to expose the specific functionality
associated with respective SoC Pins

This driver provides configuration APIs,
using them, configuration need to be done in board specific code

for ex- following code configures MFPs 107 and 108 for UART_TX/RX functionality

int board_early_init_f(void)
{
        u32 mfp_cfg[] = {
                /* Console on UART1 */
                MFP107_UART1_RXD,
                MFP108_UART1_TXD,
                MFP_EOC         /*End of configureation*/
        };
        /* configure MFP's */
        mfp_config(mfp_cfg);
        return 0;
}

Signed-off-by: Prafulla Wadaskar <prafulla@marvell.com>