libcutils: Add support for RT schedtune group

Add an SP_RT_APP group which will be used to provide minimum
capacity guarantees to RT tasks sensitive to frequency drops
such as synthesizer workloads.

Bug: 33085313
Change-Id: I07cca79e52661d1325a1db9ef3b61eb0f8d20989
Signed-off-by: Joel Fernandes <joelaf@google.com>