net: phy: Hide Micrel KSZ9021 and KSZ9031 Kconfig options

The correct option is PHY_MICREL_KSZ90X1, but some configs still
select the 9021 and 9031 options, which are deprecated.

Signed-off-by: Alexandru Gagniuc <alex.g@adaptrum.com>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>