ANDROID: GKI: Guard dynamic task_struct size feature with config option

Ensure that dynamic task_struct size feature is enabled only for GKI
platforms. With this patch, non-GKI platforms will not face build issues
anymore due to incorrect configuration earlier.

Bug: 233921394
Fixes: 5e9a8cb7 ("ANDROID: GKI: Add to task_struct size via
cmdline")
Change-Id: Ice341f4826baf8d20a3c846d55db5ea870753c7d
Signed-off-by: Sai Harshini Nimmala <quic_snimmala@quicinc.com>