mailbox: pcc: Move bulk of PCCT parsing into pcc_mbox_probe

Move the PCCT subspace parsing and allocation into pcc_mbox_probe so
that we can get rid of global PCC channel and mailbox controller data.
It also helps to make use of devm_* APIs for all the allocations.

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