net: phy: broadcom: Add Broadcom PTP hooks to bcm-phy-lib

Add 'struct bcm_ptp_private' to bcm54xx_phy_priv which points to
an optional PTP structure attached to the PHY.  This is allocated
on probe if PHY PTP support is configured, and if the driver supports
PTP for the specified PHY.

Add the bcm_ptp_probe(), bcm_ptp_config_init() and bcn_ptp_stop()
API functions to the bcm-phy library.

Signed-off-by: Jonathan Lemon <jonathan.lemon@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Acked-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>