net: stmmac: Make code changes to support dlkm compilation

Replace ethqos function calls with function pointer in stmmac.
Makefile changes to compile all ethqos files as single ko.

Change-Id: Iae8fb981b59cf14e33d31530a8798cc56c0e9926
Signed-off-by: Sneh Shah <snehshah@codeaurora.org>