In preparation for EN7581 SoC support, move en7523 in dedicated
subtarget.
This is needed as EN7581 is now 64bit but en7523 is 32bit hence have
very different kernel config.
Also rename patch to a more friendly number sequence.
Link: https://github.com/openwrt/openwrt/pull/16730
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
