hikey960.mk: set HIKEY_USES_GKI true for mainline kernel

to avoid invonvenience when forgot to set explicitly,
which will cause boot failures on the adb connections

Test: booted to homescreen with the mainline kernel
      and adb connection works

Change-Id: I07e22d831a747915e7926fba584b0665c1d3f558
Signed-off-by: Yongqin Liu <yongqin.liu@linaro.org>
1 file changed