board: starfive: Dynamic configuration of DT for 1.2A and 1.3B

The main difference between StarFive VisionFive 2 1.2A and 1.3B is gmac.
You can read the PCB version of the current board by
get_pcb_revision_from_eeprom(), and then dynamically configure the
difference of gmac in spl_perform_fixups() according to different PCB
versions, so that one DT and one defconfig can support both 1.2A and
1.3B versions, which is more user-friendly.

Signed-off-by: Yanhong Wang <yanhong.wang@starfivetech.com>
Reviewed-by: Rick Chen <rick@andestech.com>