ARM: dts: aspeed: ethanolx: Add label for the master partition

Add label "bmc" for the flash master partition. The master partition
is required for the firmware update in the OpenBMC ecosystem.

Signed-off-by: Konstantin Aladyshev <aladyshev22@gmail.com>
Link: https://lore.kernel.org/r/20230111100105.707-1-aladyshev22@gmail.com


Signed-off-by: Joel Stanley <joel@jms.id.au>