coresight: trbe: Decouple buffer base from the hardware base

coresight: trbe: Decouple buffer base from the hardware base

We always set the TRBBASER_EL1 to the base of the virtual ring
buffer. We are about to change this for working around an erratum.
So, in preparation to that, allow the driver to choose a different
base for the TRBBASER_EL1 (which is within the buffer range).

Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Mike Leach <mike.leach@linaro.org>
Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Cc: Leo Yan <leo.yan@linaro.org>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20211019163153.3692640-8-suzuki.poulose@arm.com
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>