Fix make clean for asm offset files

Automatically created assembly offset files added to CLEAN-OBJS list
for proper cleanup. This will fix following build error:
1) Build for the workstation
./conigure
make
make clean
2) Build for ARM platform
./configure --target=armv7-linux-gcc
make ==> this will fail because it uses old asm_*_offset.asm files

Change-Id: Id5275c470390ca81b8db086a15ad75af39b80703