boards: shields: add nxp_m2_wifi_bt shield

- Added new shield to add support for WIFI and BT interface.
- Added board overlay for MIMXRT1060EVKC.
- Removed mimxrt1062 overlay from shell example to avoid conflicts.
- Added seperate shield overlay for supported M.2 module to enable
 BT or WIFI or Both.
- Added default kconfigs for each BT and WIFI which enables supported
 modules and SoC as part of enabled shield through build param.
- Added shield document.

Signed-off-by: Nirav Agrawal <nirav.agrawal@nxp.com>