ixgbe/base: rework X550em PHY setup function

ixgbe/base: rework X550em PHY setup function

This patch cleans up the ixgbe_setup_internal_phy_ x550em() function as follows:
 - Renames it to ixgbe_setup_internal_phy_t_x550em to clarify that it is
   specific to copper
 - Returns an error if called for non-copper devices
 - Corrects the comments
 - Removed the LASI(Link Alarm Status Interrupt) status register checks as
   this was incorrect and never worked correctly anyway.

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