[PATCH] firmware: meson_sm: Add serial number sysfs entry

Neil Armstrong [off-list ref] writes:

The Amlogic Meson SoC Secure Monitor implements a call to retrieve an unique
SoC ID starting from the GX Family and all new families.

The serial number is simply exposed as a sysfs entry under the firmware
sysfs directory.

Signed-off-by: Neil Armstrong <redacted>

Applied to v4.20/drivers,

Thanks,

Kevin