metadata: ensure one dependency provider to be y if a package is y

metadata: ensure one dependency provider to be y if a package is y

When there are multiple packages providing a meta-package, it is
possible to to create a config where a package is selected as =y, but
all of its dependency providers are just selected as =m. This is due to
the selection statement being just

  config PACKAGE_foo
    select PACKAGE_bar if !PACKAGE_baz

which is already fulfilled by PACKAGE_bar=m. Fix this by properly
comparing the selection states:

  config PACKAGE_foo
    select PACKAGE_bar if PACKAGE_baz<PACKAGE_foo

Also invert the select conditions to improve readability.

Signed-off-by: Jonas Gorski <jonas.gorski@gmail.com>
[slightly reword commit message]
Signed-off-by: Jo-Philipp Wich <jo@mein.io>