Since linux-stable 5.10.112 commit:
1ff5359afa5e ("net: micrel: fix KS8851_MLL Kconfig")
it is not possible to select KS8851_MLL symbol.
This is because the commit adds dependency on Kconfig symbol
PTP_1588_CLOCK_OPTIONAL
which was added in Linux upstream commit:
e5f31552674e ("ethernet: fix PTP_1588_CLOCK dependencies")
And the aforementioned commit is not part of stable 5.10.112.
