mikrobus driver update patch

This Patch series is an update to the mikroBUS driver
with support for serdev devices and fixed regulator.

RFC v1 Patch : https://lkml.org/lkml/2020/7/24/518

 .
The mikrobus driver is updated to add mikrobus ports from device-tree
overlays, the debug interfaces for adding mikrobus ports through sysFS
is removed, and the driver considers the extended usage of mikrobus
port pins from their standard purposes.

change log:
        v2: support for adding mikroBUS ports from DT overlays,
        remove debug sysFS interface for adding mikrobus ports,
        consider extended pin usage/deviations from mikrobus standard
        specifications,
        use greybus CPort protocol enum instead of new protcol enums
        Fix cases of wrong indendation, ignoring return values, freeing
        allocated resources in case of errors and other style suggestions
        in v1 review.

Signed-off-by: Vaishnav M A <vaishnav@beagleboard.org>