[POWERPC] Remove ppc32's export of console_drivers

There are no in-tree uses of the export any more and in linux-next there
is a change that exports it globally which causes warnings:

WARNING: vmlinux: 'console_drivers' exported twice. Previous export was in vmlinux

and in one case (mpc85xx_defconfig) a build error:

kernel/built-in.o: In function `__crc_console_drivers':
(*ABS*+0x1eb0e6f5): multiple definition of `__crc_console_drivers'

So remove the export now.  Also, there is no longer any need to include
linux/console.h.

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>