tplink-safeloader: TP-Link EAP615-Wall v1 support

tplink-safeloader: TP-Link EAP615-Wall v1 support

Support creating images for the TP-Link EAP615-Wall v1.

Original partition layout:
  partition fs-uboot base 0x00000 size 0x80000
  partition partition-table base 0x80000 size 0x02000
  partition default-mac base 0x90000 size 0x01000
  partition support-list base 0x91000 size 0x00100
  partition product-info base 0x91100 size 0x00400
  partition soft-version base 0x92000 size 0x00100
  partition os-image base 0xa0000 size 0x380000
  partition file-system base 0x420000 size 0x970000
  partition user-config base 0xd90000 size 0x60000
  partition mutil-log base 0xf30000 size 0x80000
  partition oops base 0xfb0000 size 0x40000
  partition radio base 0xff0000 size 0x10000

In OpenWrt, the os-image and file-system partitions are merged into a
single firmware partition.

Signed-off-by: Stijn Tintel <stijn@linux-ipv6.be>
Reviewed-by: Sander Vanheule <sander@svanheule.net>