treewide: use name in define and eval lines

For consistency, use full name instead of $(PKG_NAME) in define and eval
lines for all packages.

I've seen reviews that asked to do this before, and I am asking the same
during reviews now. To avoid this in the future, fix this treewide so
when people use existing packages as example, we will not have to
request this change anymore.

This makes all packages consistent with both LEDE and OpenWrt base
repositories.

Signed-off-by: Stijn Tintel <stijn@linux-ipv6.be>

CONTRIBUTING.md

@@ -22,6 +22,7 @@ All packages you commit or submit by pull-request should follow these simple gui
 * An optional PKG_LICENSE_FILES tag including the filenames of the license-files in the source-package.
     (E.g.: PKG_LICENSE_FILES:=COPYING)
 * PKG_RELEASE should be initially set to 1 or reset to 1 if the software version is changed. You should increment it if the package itself has changed. For example, modifying a support script, changing configure options like --disable* or --enable* switches, or if you changed something in the package which causes the resulting binaries to be different. Changes like correcting md5sums, changing mirror URLs, adding a maintainer field or updating a comment or copyright year in a Makefile do not require a change to PKG_RELEASE.
+* Avoid reuse of PKG_NAME in call, define and eval lines to improve readability.
 
 #### Commits in your pull-requests should: