Add test for BANK() in constant context

test/asm/bank.asm

@@ -0,0 +1,23 @@
+def_sect: macro
+	IF _NARG == 2
+		SECTION "\1", \2
+	ELSE
+		SECTION "\1", \2, BANK[\3]
+	ENDC
+
+	PRINTV BANK("\1")
+	PRINTT "\n"
+endm
+
+ def_sect ROM0_ok,  ROM0
+ def_sect ROMX_ok,  ROMX,  42
+ def_sect ROMX_bad, ROMX
+ def_sect VRAM_ok,  VRAM,  1
+ def_sect VRAM_bad, VRAM
+ def_sect SRAM_ok,  SRAM,  4
+ def_sect SRAM_bad, SRAM
+ def_sect WRAM0_ok, WRAM0
+ def_sect WRAMX_ok, WRAMX, 7
+ def_sect WRAMX_bad,WRAMX
+ def_sect OAM_ok,   OAM
+ def_sect HRAM_ok,  HRAM