kvmtool: Makefile: remove static dependency files when make clean

After make lkvm-static & make clean, the dependency files for static
objects (.xxx.static.o.d) are not removed.

Signed-off-by: Xiaochen Shen <xiaochen.shen@intel.com>
Signed-off-by: Dimitri John Ledkov <dimitri.j.ledkov@intel.com>
Signed-off-by: James Hunt <james.o.hunt@intel.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>