ANDROID: sched: vendor hook for sched_getaffinity

Just as sched_getaffinity updates the affinity based upon the
active_mask, the vendor hook needs to be able to constrain
the task's affinity.

Introduce a hook to sched_getaffinity such that vendor modules used for
implementing Qualcomm's load tracking scheme, WALT are able to update the
affinity.

Bug: 229133948
Change-Id: I5c501e9204d4fcc6688f675a41be60ef5a2d1075
Signed-off-by: Stephen Dickey <quic_dickey@quicinc.com>
Signed-off-by: Ashay Jaiswal <quic_ashayj@quicinc.com>