make all for changed objects instead of make for each one

Some folders in kernel source tree do not have a Makefile, and when
there is a changed object under such folder, these objects can only
be rebuilt from upper directory.For exmaple: net/dccp/ccids/ccid2.o,
security/selinux/ss/ebitmap.o, and there are many others.

This patch use 'make all' to rebuilt all objects, and copy them after
that. This method does increase the kpatch-build time, but we needn't
handle special cases then.