net: phy: broadcom: update dependency condition

net: phy: broadcom: update dependency condition

The broadcom PHY driver only has to depend upon PTP_1588_CLOCK_OPTIONAL
if NETWORK_PHY_TIMESTAMPING is enabled. The PTP functionality is stubbed
in this case.

Reflect this circumstance in the dependence condition. This allows to
build the driver as a built-in module even if PTP is built as a module.

This is required to include the broadcom PHY module regardless of the
built-setting of the PTP subsystem. On ath79 (and probably more)
targets with Broadcom PHY, Gigabit operation is currently broken as the
PHY driver is only built as a module in case all kernel-packages are
built. Due to this circumstance, affected devices fall back to using the
generic PHY driver.

Signed-off-by: David Bauer <mail@david-bauer.net>
(cherry picked from commit cbce32e30c29dc69907c6f4c0ab79dd5d9a8fb28)