gator: Fix out-of-tree build

gator: Fix out-of-tree build

Fixes out-of-tree build error:
In file included from ../drivers/gpu/arm/midgard/r12p0_04rel0/mali_kbase_pm.h:28:0,
                 from ../drivers/gpu/arm/midgard/r12p0_04rel0/mali_kbase.h:49,
                 from ../drivers/gator/gator_events_mali_midgard_hw.c:25:
../drivers/gpu/arm/midgard/r12p0_04rel0/mali_kbase_hwaccess_pm.h:30:32: fatal error: mali_kbase_pm_defs.h: No such file or directory
 #include <mali_kbase_pm_defs.h>
                                ^
make[3]: *** [drivers/gator/gator_events_mali_midgard_hw.o] Error 1

Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Change-Id: I4ac47177425b120c556323ca9c4f0fb6a9bd5edd