perf arm-spe: Refactor printing string to buffer

perf arm-spe: Refactor printing string to buffer

When outputs strings to the decoding buffer with function snprintf(),
SPE decoder needs to detects if any error returns from snprintf() and if
so needs to directly bail out.  If snprintf() returns success, it needs
to update buffer pointer and reduce the buffer length so can continue to
output the next string into the consequent memory space.

This complex logics are spreading in the function arm_spe_pkt_desc() so
there has many duplicate codes for handling error detecting, increment
buffer pointer and decrement buffer size.

To avoid the duplicate code, this patch introduces a new helper function
arm_spe_pkt_out_string() which is used to wrap up the complex logics,
and it's used by the caller arm_spe_pkt_desc().  This patch moves the
variable 'blen' as the function's local variable so allows to remove
the unnecessary braces and improve the readability.

This patch simplifies the return value for arm_spe_pkt_desc(): '0' means
success and other values mean an error has occurred.  To realize this,
it relies on arm_spe_pkt_out_string()'s parameter 'err', the 'err' is a
cumulative value, returns its final value if printing buffer is called
for one time or multiple times.  Finally, the error is handled in a
central place, rather than directly bailing out in switch-cases, it
returns error at the end of arm_spe_pkt_desc().

This patch changes the caller arm_spe_dump() to respect the updated
return value semantics of arm_spe_pkt_desc().

Suggested-by: Dave Martin <Dave.Martin@arm.com>
Signed-off-by: Leo Yan <leo.yan@linaro.org>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Dave Martin <Dave.Martin@arm.com>
Acked-by: Will Deacon <will@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Al Grant <Al.Grant@arm.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@arm.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: John Garry <john.garry@huawei.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Wei Li <liwei391@huawei.com>
Link: https://lore.kernel.org/r/20201119152441.6972-2-leo.yan@linaro.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>