perf arm-spe: Rename arm_spe__synth_data_source_generic()

perf arm-spe: Rename arm_spe__synth_data_source_generic()

The arm_spe__synth_data_source_generic() function is invoked when the
tool detects that CPUs do not support data source packets and falls back
to synthesizing only the memory level.

Rename it to arm_spe__synth_memory_level() for better reflecting its
purpose.

Signed-off-by: Leo Yan <leo.yan@arm.com>
Reviewed-by: James Clark <james.clark@linaro.org>
Link: https://lore.kernel.org/r/20241003185322.192357-2-leo.yan@arm.com
Signed-off-by: Namhyung Kim <namhyung@kernel.org>