drivers: most: add character device interface driver

This patch adds the character device (cdev) driver source file
most_cdev.c and modifies the Makefiles and Kconfigs accordingly.

Signed-off-by: Christian Gromm <christian.gromm@microchip.com>
Link: https://lore.kernel.org/r/1597922595-27493-1-git-send-email-christian.gromm@microchip.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>