perf build: Ensure sysreg-defs Makefile respects output dir

perf build: Ensure sysreg-defs Makefile respects output dir

Currently the sysreg-defs are written out to the source tree
unconditionally, ignoring the specified output directory. Correct the
build rule to emit the header to the output directory. Opportunistically
reorganize the rules to avoid interleaving with the set of beauty make
rules.

Reported-by: Ian Rogers <irogers@google.com>
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
Link: https://lore.kernel.org/r/20231121192956.919380-3-oliver.upton@linux.dev
Signed-off-by: Namhyung Kim <namhyung@kernel.org>