MAINTAINERS: mark stmmac ethernet as an Orphan

MAINTAINERS: mark stmmac ethernet as an Orphan

I tried a couple of things to reinvigorate the stmmac maintainers
over the last few years but with little effect. The maintainers
are not active, let the MAINTAINERS file reflect reality.
The Synopsys IP this driver supports is very popular we need
a solid maintainer to deal with the complexity of the driver.

gitdm missingmaints says:

Subsystem STMMAC ETHERNET DRIVER
  Changes 344 / 978 (35%)
  Last activity: 2020-05-01
  Alexandre Torgue <alexandre.torgue@foss.st.com>:
    Tags 1bb694e20839 2020-05-01 00:00:00 1
  Jose Abreu <joabreu@synopsys.com>:
  Top reviewers:
    [75]: horms@kernel.org
    [49]: andrew@lunn.ch
    [46]: fancer.lancer@gmail.com
  INACTIVE MAINTAINER Jose Abreu <joabreu@synopsys.com>

Acked-by: Alexandre Torgue <alexandre.torgue@foss.st.com>
Link: https://patch.msgid.link/20250108155242.2575530-5-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>