package: fix patching procedure for host packages

The patching procedure was using $($(NOHOSTPKG)_NAME) to find the name
of the package without the host- prefix for host packages, which is
needed to find the package directory and the prefix of the patches.

However, this $($(NOHOSTPKG)_NAME) variable is empty when there is
only an host variant for the package and no target variant for it.

Therefore, instead of using this $($(NOHOSTPKG)_NAME) variable, we now
use a new $(RAWNAME) variable, which is always the name of the package
without the host- prefix, even for host packages.

Thanks to Yann E. Morin for providing the tip on using patsubst
instead of subst.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>