meta-tizen: efl: correct "first-build" issue

meta-tizen: efl: correct "first-build" issue

efl first build failed because capi-system-sensor was missing. This was
due to the dependency on capi-system-sensor being overridden in
efl-extraconf.inc.

Also clean efl-extraconf.inc and add a few comments.

Bug-Tizen: BTY-45
Change-Id: Ica35657297c65b4b65f29c2042e0197ff680d0cc
(From meta-tizen rev: 3f5e463a3f8ccebee1a83eda630b9a958a737ca4)

Signed-off-by: Kévin THIERRY <kevin.thierry@open.eurogiciel.org>
Signed-off-by: Patrick Ohly <patrick.ohly@intel.com>