powerpc: Remove unused vgacon_remap_base & fix build break

The build is broken with CONFIG_PPC32=y, CONFIG_FB_VGA16=y and
CONFIG_VGA_CONSOLE=n.

The problem is that vgacon_remap_base is not defined. It's used in:

    #define VGA_MAP_MEM(x,s) (x + vgacon_remap_base)

Which is used in the vga16fb.c code.

Digging down it seems vgacon_remap_base is never initialised. It used to
be, back in arch/ppc (pplus.c and prep_setup.c), but none of that code
ever made it to arch/powerpc.

So given it's been unused for >6 years, remove it.

Whether vga16fb.c works on 32-bit is another question, but this patch
shouldn't affect it.
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/vga.h

@@ -38,12 +38,10 @@ static inline u16 scr_readw(volatile const u16 *addr)
 
 #endif /* !CONFIG_VGA_CONSOLE && !CONFIG_MDA_CONSOLE */
 
-extern unsigned long vgacon_remap_base;
-
 #ifdef __powerpc64__
 #define VGA_MAP_MEM(x,s) ((unsigned long) ioremap((x), s))
 #else
-#define VGA_MAP_MEM(x,s) (x + vgacon_remap_base)
+#define VGA_MAP_MEM(x,s) (x)
 #endif
 
 #define vga_readb(x) (*(x))

arch/powerpc/kernel/setup_32.c

@@ -52,11 +52,6 @@ unsigned long ISA_DMA_THRESHOLD;
 unsigned int DMA_MODE_READ;
 unsigned int DMA_MODE_WRITE;
 
-#ifdef CONFIG_VGA_CONSOLE
-unsigned long vgacon_remap_base;
-EXPORT_SYMBOL(vgacon_remap_base);
-#endif
-
 /*
  * These are used in binfmt_elf.c to put aux entries on the stack
  * for each elf executable being started.