Bluetooth: CAP: Add support for long read/write

Add support for reading and writing long values (> MTU)
when using the CAP API.

This change does make it slightly slower to execute the
CAP procedures as it is now done on a one-by-one basis,
which affect multi-ACL setups, but that also means
that the buffer requirements for CAP will generally be lower.

There is still room for improvement as we can perform the BAP
operations in parallel on each ACl, which should return this to
its former performance.

Signed-off-by: Emil Gydesen <emil.gydesen@nordicsemi.no>