lib.sh: more unified config handling

replace it with logic that simply uses "." to load
files directly. for this, "vcfg" is added as a variable
in coreboot target.cfg files, referring to a directory
in config/vendor/ containing a file named pkg.cfg, and
this file then contains the same variables as the
erstwhile config/vendor/sources

config/git files are now directories, also containing
pkg.cfg files each with the same variables as before,
such as repository link and commit hash

this change results in a noticeable reduction in code
complexity within the build system.

unified reading of config files: new function setcfg()
added to lib.sh

setcfg checks if a config exists. if a 2nd argument is
passed, it is used as a return value for eval, otherwise
a string calling err is passed. setcfg output is passed
through eval, to set strings based on config; eval must
be used, so that the variables are set within the same
scope, otherwise they'd be set within setcfg which could
lead to some whacky results.

there's still a bit more more to do, but this single change
results in a substantial reduction in code complexity.

Signed-off-by: Leah Rowe <leah@libreboot.org>

config/vendor/hp9470m/pkg.cfg

@@ -0,0 +1,6 @@
+DL_hash="4dc908050c91c1227645c900ddee88652937540af4ba222b0239b7f459f260cdf6e5e8113ac14e5543d00cf53abdd6c7bd23e61f690de1ce45a3709a30cbb91c"
+DL_url="https://download.lenovo.com/pccbbs/mobiles/g1rg24ww.exe"
+DL_url_bkup="https://web.archive.org/web/20210706183911/https://download.lenovo.com/pccbbs/mobiles/g1rg24ww.exe"
+EC_hash="563422bf5420da18b89439f28a38ea28a175f0ad3588f0f5ea39b08dfdd14c8d513cbf11c2125ec3869fc3b7222c7dc3d111415185ea9b73f41410b1b57f13bd"
+EC_url="https://ftp.hp.com/pub/softpaq/sp96001-96500/sp96090.exe"
+EC_url_bkup="http://web.archive.org/web/20220504072602/https://ftp.ext.hp.com/pub/softpaq/sp96001-96500/sp96090.exe"