drivers: ethernet: phy: Add OPEN Alliance TC14 PLCA generic lib support

10BASE-T1S PHYs can operate in either CSMA/CD or PLCA mode. PLCA mode
needs some set of parameters like node id, node count, max burst count,
burst timer and TO (Transmit Oppertunity) timer to be configured. OPEN
Alliance TC14 specification defined a set of PLCA registers to configure
PLCA mode. The below APIs are implemented for PLCA mode.

genphy_set_plca_cfg() - to configure PLCA settings.
genphy_get_plca_cfg() - to get the configured PLCA settings.
genphy_get_plca_sts() - to get the PLCA status like active or inactive.

These APIs are implemented as generic library so that all 10BASE-T1S
PHYs can use these APIs to configure/access PLCA settings to avoid
duplication of code.

Signed-off-by: Parthiban Veerasooran <parthiban.veerasooran@microchip.com>