package/Config.in: change postgresql condition

package/Config.in: change postgresql condition

The condition around postgis was added to make a sort of submenu of the
postgresql extensions under postgresql itself. However, such a condition
should be on BR2_PACKAGE_POSTGRESQL, not on its suboption
BR2_PACKAGE_POSTGRESQL_FULL.

Change the condition in package/Config.in to BR2_PACKAGE_POSTGRESQL, and
move the BR2_PACKAGE_POSTGRESQL_FULL condition to
package/postgis/Config.in.

Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>