stmmac: intel: Add PSE and PCH PTP clock source selection

Intel mGbE variant implemented in EHL and TGL can be set to select
different clock frequency based on GPO bits in MAC_GPIO_STATUS register.

We introduce a new "void (*ptp_clk_freq_config)(void *priv)" in platform
data so that if a platform is required to configure the frequency of clock
source, in this case Intel mGBE does, the platform-specific configuration
of the PTP clock setting is done when stmmac_ptp_register() is called.

Signed-off-by: Wong, Vee Khee <vee.khee.wong@intel.com>
Signed-off-by: Voon Weifeng <weifeng.voon@intel.com>
Co-developed-by: Ong Boon Leong <boon.leong.ong@intel.com>
Signed-off-by: Ong Boon Leong <boon.leong.ong@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>