support/dependencies/check-host-cmake.mk: gerbera needs cmake 3.14+
Fixes:
http://autobuild.buildroot.net/results/871/8717612ae32cc491b868f37fbbc960c16b562877/
Since the security bump to gerbera 1.6.4, gerbera now needs cmake 3.14+,
whereas Buildroot currently enforces 3.10+.
As a fix, bump the requirement to 3.14+ when gerbera is enabled.
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>