tests/i915/gem_lmem_swapping: run only for discrete platform

Testsuit only meant to be run on discrete platforms and skip
with right reason on other platforms.

changes since V1:
	- Change position of gem_has_lmem(i915) check - Zbigniew

Reviewed-by: Zbigniew Kempczyński <zbigniew.kempczynski@intel.com>
Signed-off-by: Tejas Upadhyay <tejaskumarx.surendrakumar.upadhyay@intel.com>