net: phy: Add support for all targets which requires MANUAL_RELOC

Targets with CONFIG_NEEDS_MANUAL_RELOC do not use REL/RELA
relocation (mostly only GOT) where functions aray are not
updated. This patch is fixing function pointers passed to phy_register
function.
This patch was tested on Microblaze architecture.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>