ANDROID: GKI: Enable the option to alter task_struct size dynamically

Enable the config option that allows for dynamic sizing of the
task_struct. Once config option is enabled, ensure that
arch_task_struct_size is initialized to hold a valid task_struct size.
The motivation behind this change is to reduce the static memory added to
the task_struct to accommodate vendor data.

Bug: 233921394
Signed-off-by: Sai Harshini Nimmala <quic_snimmala@quicinc.com>
Change-Id: Iebc422ba4c650864f470078220b99546e56302f3