package/pkg-generic: handle host-ccache as a regular dependency

package/pkg-generic: handle host-ccache as a regular dependency

This moves the host-ccache dependency handling from
DEPENDENCIES_HOST_PREREQ to a proper package dependency. When
BR2_CCACHE=y, we add host-ccache as a regular dependency of all
packages except:

 - The extractor packages host-tar, host-xz and host-lzip

 - host-ccache itself

 - host-skeleton, because all packages depend on it

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Tested-by: Matt Weber <matthew.weber@rockwellcollins.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>