package/pkg-cmake.mk: rename _INSTALL_HOST_OPTS -> _INSTALL_OPTS

package/pkg-cmake.mk: rename _INSTALL_HOST_OPTS -> _INSTALL_OPTS

This patch renames, consistently with the other package
infrastructures, the _INSTALL_OPTS variable for host CMake-based
package.

As mentioned in [1], no host-cmake-package uses this variable so far;
so it is a safe rename.

[1] http://lists.busybox.net/pipermail/buildroot/2014-October/107712.html

Reported-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Samuel Martin <s.martin49@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>