linux: drop smsc95xx-mac patch
smsc95xx-mac used to have problems with booting over NFS due to firmware
problem. This patch had been rejected upstream [1].
Since then, firmware people have fixed their firmware, from as far as
3 years ago, since rpi-firmware pulled that update in 2017-02-26 [2][3]
Drop this patch in all of our kernel series.
1: https://lore.kernel.org/linux-omap/1277367254-9345-1-git-send-email-s-jan@ti.com/T/#u
2: https://github.com/raspberrypi/firmware/issues/613#issuecomment-282681283
3: 411288a7e3
8fc6facbb1