rockchip: board: puma_rk3399: add support for serial# and cpuid# via efuses

With our efuse driver for the RK3399 ready, we can add the
board-specific code that consumes the cpuid from the efuse block and
postprocesses it into the system serial (using the same CRC32 based
derivation as in Linux).

We expose the cpuid via two distinct environment variables:
   serial# - the serial number, as derived in Linux
   cpuid#  - the raw 16 byte CPU id field from the fuse block

Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Acked-by: Simon Glass <sjg@chromium.org>