mmc-utils: rely on common variables

Instead of assigning various variables ourself, rely on the common logic
provided by "packaging framework". This brings this package in sync with
other ones which also use git repos as source, dates and commit ids as
version etc. This results also in using xz for tarballs. While at,
populate the PKG_MIRROR_HASH.

Thanks @diizzyy for suggesting these improvements.

Signed-off-by: Michael Heimpold <mhei@heimpold.de>

utils/mmc-utils/Makefile

@@ -8,14 +8,13 @@
 include $(TOPDIR)/rules.mk
 
 PKG_NAME:=mmc-utils
-PKG_VERSION=2017-03-20-$(PKG_SOURCE_VERSION)
 PKG_RELEASE:=1
 
 PKG_SOURCE_PROTO:=git
 PKG_SOURCE_URL:=https://git.kernel.org/pub/scm/linux/kernel/git/cjb/mmc-utils.git
+PKG_SOURCE_DATE:=2017-03-20
 PKG_SOURCE_VERSION:=37c86e60c0442fef570b75cd81aeb1db4d0cbafd
-PKG_SOURCE_SUBDIR:=$(PKG_NAME)-$(PKG_SOURCE_VERSION)
-PKG_SOURCE:=$(PKG_NAME)-$(PKG_SOURCE_VERSION).tar.gz
+PKG_MIRROR_HASH:=fc49fce4f592ffdc2a9c8f453ea96b28eb3ece0c6303ed73462cc61fb5b63318
 
 PKG_LICENSE:=GPL-2.0
 PKG_LICENSE_FILES:=
@@ -23,7 +22,6 @@ PKG_LICENSE_FILES:=
 PKG_MAINTAINER:=Michael Heimpold <mhei@heimpold.de>
 
 PKG_BUILD_PARALLEL:=1
-PKG_BUILD_DIR:=$(BUILD_DIR)/$(PKG_NAME)-$(PKG_SOURCE_VERSION)
 
 include $(INCLUDE_DIR)/package.mk