tests/kms_cursor_edge_walk: Limit the execution to two pipes

To optimize the test execution time, limit the execution to
two (first & last) pipes. This patch will also provide an
option (command line flag '--extended') to execute on all
pipes.

Example:
./kms_cursor_edge_walk --extended --run-subtest 64x64-left-edge

Signed-off-by: Bhanuprakash Modem <bhanuprakash.modem@intel.com>
Signed-off-by: Nidhi Gupta <nidhi1.gupta@intel.com>
Reviewed-by: Karthik B S <karthik.b.s@intel.com>