samples: gnss: Move sample under a subdirectory

So that upcoming RTK sample can be grouped alongside the existing
gnss basic.

Signed-off-by: Luis Ubieda <luisf@croxel.com>

Author: ubieda

samples/drivers/gnss/CMakeLists.txt renamed to samples/drivers/gnss/basic/CMakeLists.txt

@@ -2,9 +2,9 @@
 # SPDX-License-Identifier: Apache-2.0
 
 sample:
-  name: GNSS sample
+  name: GNSS basic sample
 tests:
-  sample.drivers.gnss:
+  sample.drivers.gnss.basic:
     tags:
       - drivers
       - gnss