ARM: prom.h: Fix build error by removing unneeded header file

Fix the following build error:

  CC [M]  fs/udf/balloc.o
In file included from /home/fabio/next/linux-next/arch/arm/include/asm/prom.h:16,
                 from include/linux/of.h:140,
                 from include/asm-generic/gpio.h:7,
                 from arch/arm/plat-mxc/include/mach/irqs.h:14,
                 from /home/fabio/next/linux-next/arch/arm/include/asm/irq.h:4,
                 from /home/fabio/next/linux-next/arch/arm/include/asm/hardirq.h:6,
                 from include/linux/hardirq.h:7,
                 from include/linux/highmem.h:8,
                 from include/linux/pagemap.h:10,
                 from include/linux/buffer_head.h:13,
                 from fs/udf/udfdecl.h:11,
                 from fs/udf/balloc.c:22:
/home/fabio/next/linux-next/arch/arm/include/asm/setup.h:146: error: redefinition of 'struct tag'

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
[grant.likely: fix build failure on drivers/of/fdt.c]
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>