Make packaging easier

Improves a few things to make it easier to package mesaflash
e.g. as an rpm package:

 - Allows to honor CFLAGS passed from command line,
 - Do not need to run make install from 'root' user,
 - Do not hardcode include directory,
 - Use pkg-config to determine compiler options for using libcpi.

As this change is fully backward compatible in order to use new
features it is needed to set the followings variables:
  - CFLAGS - usually done by linux distribution,
  - DEBUG - set to empty as CFLAGS should contain everything needed,
  - OWNERSHIP - set to empty - (e.g. rpm will set it correctly for you).

Example:
 $ CFLAGS="distribution specific list of options" DEBUG="" OWNERSHIP="" make

Signed-off-by: Damian Wrobel <dwrobel@ertelnet.rybnik.pl>