fix Makefile chmod (644)
replace MD5SUM with HASH
add PKG_MIRROR_HASH when PKG_SOURCE_PROTO:=git

(PKG_SOURCE_PROTO:=svn tarballs are not reproducible for now)

Signed-off-by: Etienne Champetier <champetier.etienne@gmail.com>

Part of a wider housekeeping effort on the packages repository.

Signed-off-by: Alberto Bursi <alberto.bursi@outlook.it>

Signed-off-by: Yunfan Jiang <jyf1987@gmail.com>