Refactor file writing - make configdata.pm the info center for "reconf"

Now that configdata.pm is the centre of information, use that instead
of Makefile to figure out reconfiguration parameters.  This will help
future development with different Makefile file names.

The code to read necessary configuration data from Makefile is retained
for an easy transition to configdata.pm based information gathering.  It
will be removed later on.

This change includes moving the variable $cross_compile_prefix to %config.

Reviewed-by: Rich Salz <rsalz@openssl.org>
Reviewed-by: Viktor Dukhovni <viktor@openssl.org>