mcelog: new package

[Thomas:
  - use "make install", which allows to remove the custom installation
    logic in mcelog.mk.
  - no need to explicitly pass CFLAGS and CPPFLAGS when doing the
    build, since those definitions are already part of
    $(TARGET_CONFIGURE_OPTS).]

Signed-off-by: Romain Naour <romain.naour@openwide.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>