arm64: dts: ti: iot2050: Add support for M.2 variant

The M.2 variant comes with 2 slots, one B-keyed and another one E-keyed.
They are configured by the firmware during startup. Also the device tree
will be adjusted according to the detect or manually configured
interface mode by the firmware. The kernel only carries a single
configuration as base device tree. It has to be built with a symbols
node so that the firmware can apply overlays for the connector modes.

Signed-off-by: chao zeng <chao.zeng@siemens.com>
[Jan: refactored to a single DT]
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Reviewed-by: Siddharth Vadapalli <s-vadapalli@ti.com>
Link: https://lore.kernel.org/r/878e3a023767b5a6d9d2cff09015678aaba13fce.1674110442.git.jan.kiszka@siemens.com


Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>