d_bg_w_kcol work

[caseif]

This PR includes a bit of work on d_bg_w_kcol functions.

[decomp-dev]

Report for GZ2E01 (e0b1fe9 - 1de5caf)

📈 Matched code: 76.43% (+0.01%, +876 bytes)

✅ 1 new match

Unit	Function	Bytes	Before	After
framework/d/d_bg_w_kcol	dBgWKCol::RoofChk(dBgS_RoofChk*)	+873	0.46%	100.00%

📈 2 improvements in unmatched functions

Unit	Function	Bytes	Before	After
framework/d/d_bg_w_kcol	dBgWKCol::ShdwDraw(cBgS_ShdwDraw*)	+1362	0.29%	99.52%
framework/d/d_bg_w_kcol	dBgWKCol::SplGrpChk(dBgS_SplGrpChk*)	+863	0.46%	99.36%