mailbox: pcc: Add support for PCCT extended PCC subspaces(type 3/4)

With all the plumbing in place to avoid accessing PCCT type and other
fields directly from the PCCT table all the time, let us now add the
support for extended PCC subspaces(type 3 and 4).

Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>