drivers: mfd: Add NXP LP Flexcomm driver

1. This driver allows to configure the Low Power Flexcomm
   interface as a UART, SPI or I2C device.
2. Manages the interrupts and dispatches it to the
   appropriate device driver.
3. A Flexcomm interface can be configured to be used as
   I2C and UART device. However a SPI device cannot be used
   concurrently with I2C or UART. Add checks for this feature.

Signed-off-by: Mahesh Mahadevan <mahesh.mahadevan@nxp.com>