Add support for Moxa UC-2101 open platform

The UC-2101 computing platform is designed for industrial embedded
data acquisition and processing applications.

The features of UC-2101 are:
* eMMC
* SPI flash
* 1x LAN
* 1x RS-232/422/485 ports, software-selectable
* EEPROM
* TPM 2.0
* Watchdog
* RTC
* User gpio-keys
* User LEDs
* User button
Signed-off-by: Wes Huang (黃淵河) <wes.huang@moxa.com>
Signed-off-by: Fero JD Zhou (周俊達) <FeroJD.Zhou@moxa.com>
Signed-off-by: SZ Lin (林上智) <sz.lin@moxa.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>