Use labels instead of constants for HRAM

Use explicit ldh instruction to access HRAM locations, don't rely on optimizing ld

engine/gfx/player_gfx.asm

@@ -28,11 +28,11 @@ MovePlayerPic:
 	push hl
 	push de
 	xor a
-	ld [hBGMapMode], a
+	ldh [hBGMapMode], a
 	lb bc, 7, 7
 	predef PlaceGraphic
 	xor a
-	ld [hBGMapThird], a
+	ldh [hBGMapThird], a
 	call WaitBGMap
 	call DelayFrame
 	pop de
@@ -147,7 +147,7 @@ GetChrisBackpic:
 HOF_LoadTrainerFrontpic:
 	call WaitBGMap
 	xor a
-	ld [hBGMapMode], a
+	ldh [hBGMapMode], a
 	ld e, 0
 	ld a, [wPlayerGender]
 	bit PLAYERGENDER_FEMALE_F, a
@@ -170,7 +170,7 @@ HOF_LoadTrainerFrontpic:
 	call Get2bpp
 	call WaitBGMap
 	ld a, $1
-	ld [hBGMapMode], a
+	ldh [hBGMapMode], a
 	ret
 
 DrawIntroPlayerPic:
@@ -200,7 +200,7 @@ DrawIntroPlayerPic:
 
 ; Draw
 	xor a
-	ld [hGraphicStartTile], a
+	ldh [hGraphicStartTile], a
 	hlcoord 6, 4
 	lb bc, 7, 7
 	predef PlaceGraphic