Felix Singer 7f50bcca93 doc/mainboard/index: Deduplicate menu points for T530 and W530

Both mainboards have the same documentation. Instead of having two list
items referring to the same document, just merge the two items.

This fixes the following Sphinx warning:

  WARNING: duplicated entry found in toctree: mainboard/lenovo/w530

Change-Id: I4140b34db01b1d5f47a39b9c1e33405e7789de63
Signed-off-by: Felix Singer <felixsinger@posteo.net>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/77503
Reviewed-by: Nicholas Chin <nic.c3.14@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

2023-08-27 11:15:00 +00:00