packages: rename FOO_INSTALL_STAGING_OPT into FOO_INSTALL_STAGING_OPTS

packages: rename FOO_INSTALL_STAGING_OPT into FOO_INSTALL_STAGING_OPTS

To be consistent with the recent change of FOO_MAKE_OPT into FOO_MAKE_OPTS,
make the same change for FOO_INSTALL_STAGING_OPT.

Sed command used:
   find * -type f | xargs sed -i 's#_INSTALL_STAGING_OPT\>#&S#g'

Signed-off-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>