Add support to read SFR's read-only registers providing the SoC
Serial Numbers (SN0+SN1) to userspace.

~ #  hexdump -n 8  -e'"%d\n"' /sys/bus/nvmem/devices/atmel-sfr0/nvmem
959527243
371539274

Signed-off-by: Kamel Bouhara <[email protected]>
Tested-by: Tudor Ambarus <[email protected]>
Reviewed-by: Tudor Ambarus <[email protected]>
Link: https://lore.kernel.org/r/[email protected]


Signed-off-by: Alexandre Belloni <[email protected]>