perf cs-etm: Refactor initialisation of kernel start address

perf cs-etm: Refactor initialisation of kernel start address

The kernel start address is already cached in the machine struct once it
is initialised, so storing it in the cs_etm struct is unnecessary.

It also depends on kernel maps being available to be initialised.
Therefore cs_etm__setup_queues() isn't an appropriate place to call it
because it could be called before processing starts. It would be better
to initialise it at the point when it is needed, then we can be sure
that all the necessary maps are available. Also by calling
machine__kernel_start() multiple times it can be initialised at some
point, even if it failed to initialise previously due to missing maps.

In a later commit cs_etm__setup_queues() will be moved which is the
motivation for this change.

Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: James Clark <james.clark@arm.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Al Grant <al.grant@arm.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: John Garry <john.garry@huawei.com>
Cc: Leo Yan <leo.yan@linaro.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mike Leach <mike.leach@linaro.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Suzuki Poulouse <suzuki.poulose@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org
Cc: coresight@lists.linaro.org
Link: https://lore.kernel.org/r/20210721150202.32065-2-james.clark@arm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>