NFC: nci: add generic uart support

Some NFC controller supports UART as host interface.
As with SPI, a lot of code can be shared between vendor
drivers. This patch add the generic support of UART and
provides some extension API for vendor specific needs.

This code is strongly inspired by the Bluetooth HCI ldisc
implementation. NCI UART vendor drivers will have to register
themselves to this layer via nci_uart_register.

Underlying tty will have to be configured from user land
thanks to an ioctl.

Signed-off-by: Vincent Cuissard <cuissard@marvell.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>