rc2014: adapt to new RomWBW memory layout

RomWBW version 3.4 changed the memory layout, putting the HBIOS working
copy into RAM bank 0. To prevent the Fuzix loader from overwriting
HBIOS, store data for bank 0 temporarily in bank 4. Copy bank 4 to bank
0 immediately before starting the kernel, when no more RomWBW calls are
needed.

This works with older RomWBW versions as well, which had HBIOS in nRAM-2
and lower banks were free to use.

Tested with RomWBW 3.2, 3.4, 3.5-dev.101 on Zed Pro.

Kernel/platform/platform-rc2014/boot-romwbw.s

@@ -85,10 +85,10 @@ bootit:
 	ld hl,#0x8000		; Don't copy first 256 bytes over
 	ld de,#0x4000
 	ld bc,#0x4000		; We've loaded 0000-4000
-	ld a,#32
+	ld a,#40
 
 	di
-	out (MPGSEL_1),a	; Low bank at 0x4000 please
+	out (MPGSEL_1),a	; Bank 4 first 16K at 0x4000
 	ldir
 
 	;
@@ -102,8 +102,9 @@ bootit:
 	ld hl,#0x8000		; Move it into place
 	ld de,#0x4000
 	ld bc,#0x4000
-	ld a,#33
-	out (MPGSEL_1),a	; Second kernel bank at 0x4000 please
+	ld a,#41
+	di
+	out (MPGSEL_1),a	; Bank 4 second 16K at 0x4000
 	ldir
 	pop bc
 
@@ -207,6 +208,28 @@ bootit:
 	out (MPGSEL_1),a
 	ldir
 
+	;
+	;	Copy from bank 4 to bank 0
+	;
+	ld hl,#0x4000
+	ld de,#0x0000
+	ld bc,#0x4000
+	ld a,#40
+	out (MPGSEL_1),a
+	ld a,#32
+	out (MPGSEL_0),a
+	ldir
+
+	; page 41 to page 33
+	ld hl,#0x4000
+	ld de,#0x0000
+	ld bc,#0x4000
+	ld a,#41
+	out (MPGSEL_1),a
+	ld a,#33
+	out (MPGSEL_0),a
+	ldir
+
 	;
 	;	Map the kernel low 16K block and jump into it
 	;