ARM: mstar: Unify common parts of BreadBee boards into a dtsi

The BreadBee and the BreadBee Crust are the same PCB with a different
SoC mounted. There are two top level dts to handle this.

To avoid deduplicating the parts that are more related to the PCB than
the SoC (i.e. the voltage regs and LEDs) add a common dtsi that can
be included in both top level dts.

Signed-off-by: Daniel Palmer <daniel@0x0f.com>
Link: https://lore.kernel.org/r/20201224020354.2212037-1-daniel@0x0f.com

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Signed-off-by: Arnd Bergmann <arnd@arndb.de>