Refactor section assignment in linker

Deduplicates and generalises a lot of code in assign.c:

- Replace area_AllocAbs*AnyBank() with area_AllocAbsAnyBank() function
that accepts a section type parameter
- Replace area_Alloc*AnyBank() with area_AllocAnyBank()
- Replace FindLargest*() with FindLargestSection()
- Replace Assign*Sections() with AssignBankedSections()
- Add VerifyAndSetBank(), which enables bank checks (and addition with
BANK_*) to be centralised
- Refactor the initialisation of AssignSections(), removing some magic
numbers and only setting MaxAvail[i] once
- Overhaul the duplicated cases throughout AssignSections()

include/link/assign.h

@@ -5,13 +5,26 @@
 
 enum eBankDefine {
 	BANK_ROM0 = 0,
+	BANK_ROMX,
 	BANK_WRAM0 = 512,
 	BANK_WRAMX,
 	BANK_VRAM = 520,
 	BANK_HRAM = 522,
 	BANK_SRAM = 523
 };
-#define MAXBANKS	527
+
+enum eBankCount {
+	BANK_COUNT_ROM0 = 1,
+	BANK_COUNT_ROMX = 511,
+	BANK_COUNT_WRAM0 = 1,
+	BANK_COUNT_WRAMX = 7,
+	BANK_COUNT_VRAM = 2,
+	BANK_COUNT_HRAM = 1,
+	BANK_COUNT_SRAM = 4
+};
+
+#define MAXBANKS	(BANK_COUNT_ROM0 + BANK_COUNT_ROMX + BANK_COUNT_WRAM0 + BANK_COUNT_WRAMX \
+					+ BANK_COUNT_VRAM + BANK_COUNT_HRAM + BANK_COUNT_SRAM)
 
 extern SLONG area_Avail(SLONG bank);
 extern void AssignSections(void);