ixgbe/base: add X550em PHY interrupt and forced speeds

ixgbe/base: add X550em PHY interrupt and forced speeds

This patch adds x550em external PHY interrupt and forced 1G/10G
support. Support includes enabling and handling Link Status
Change and Thermal Sensor interrupt. ixgbe_handle_lasi has been added
to the API for handling the interrupts received from x550em PHY.
ixgbe_enable_lasi_ext_t_x550em and ixgbe_get_lasi_ext_t_x550em have been
added to X550em to enable mask and check interrupt flags for x550em PHY.

Forced 1G/10G link speed is handled via ixgbe_setup_mac_link_t_X550em.
ixgbe_setup_mac_link_t_X550em sets up the internal PHY and
external PHY link to either 10G or 1G based on the user selected auto
advertised link speed setting. Then sets up the external PHY auto
advertised link speed.

Signed-off-by: Wenzhuo Lu <wenzhuo.lu@intel.com>
Acked-by: Helin Zhang <helin.zhang@intel.com>