net: stmmac: qcom-ethqos: add ethqos_pcs_set_inband()

Add ethqos_pcs_set_inband() to improve readability, and to allow future
changes when phylink PCS support is properly merged.

Reviewed-by: Andrew Halaney <ahalaney@redhat.com>
Tested-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org> # sa8775p-ride-r3
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/E1uPkbO-004EyA-EU@rmk-PC.armlinux.org.uk


Signed-off-by: Jakub Kicinski <kuba@kernel.org>