ARC: [plat-hsdk] Get rid of inappropriate PHY settings

Initial bring-up of the platform was done on FPGA prototype
where TI's DP83867 PHY was used. And so some specific PHY
options were added.

Just to confirm this is what we get on FPGA prototype in the bootlog:
| TI DP83867 stmmac-0:00: attached PHY driver [TI DP83867] ...

On real board though we have Micrel KZS9031 PHY and we even have
CONFIG_MICREL_PHY=y set in hsdk_defconfig. That's what we see in the bootlog:
| Micrel KSZ9031 Gigabit PHY stmmac-0:00: ...

So essentially all TI-related bits have to go away.

Cc: Rob Herring <robh+dt@kernel.org>
Acked-by: Trent Piepho <tpiepho@impinj.com>
Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>