Code refactor and bug fixes related to bgm. #2055

Job	Run time
build	1m 13s
build-lang	29s
build-variants (EXTRA_FEATURES=0, PADEMU=0)	1m 12s
build-debug (iopcore_debug, :main)	1m 19s
build-variants (EXTRA_FEATURES=0, PADEMU=1)	1m 16s
build-debug (ingame_debug, :main)	1m 26s
build-variants (EXTRA_FEATURES=1, PADEMU=0)	1m 14s
build-variants (EXTRA_FEATURES=1, PADEMU=1)	1m 14s
build-debug (eesio_debug, :main)	1m 24s
build-debug (iopcore_ppctty_debug, :main)	1m 20s
build-debug (ingame_ppctty_debug, :main)	1m 24s
build-debug (DTL_T10000=1, :main)	1m 23s
merge-variants	8s
release	0s
merge-debug	6s
	15m 8s

Provide feedback