ramips: use on-flash partition table for Sercomm BZV/CHJ

ramips: use on-flash partition table for Sercomm BZV/CHJ

These devices have a partition table stored in flash, which compensates
for any pre-existing bad blocks by enlarging the respective partition.
This means that the current static partition table is only correct for
devices without any bad blocks.

Typical results of this mismatch are degraded wireless performance and
wrong MAC addresses, when the factory partition is shifted due to a bad
block somewhere before it. If there is a bad block already before the
ubi partition, then OpenWrt may not run at all because the kernel can't
find the rootfs.

Use the on-flash partition table to fix these issues. Replace the two
reserved partitions by the full partition list, as the driver does not
allow merging them.

Signed-off-by: Jan Hoffmann <jan@3e8.eu>