ARM: OMAP2+: Remove board-omap4panda.c

We can now boot with device tree. If you don't want to update u-boot,
you can boot with appended DTB with the following instructions:

1. Make sure you have the appended DTB support in .config

   CONFIG_ARM_APPENDED_DTB=y
   CONFIG_ARM_ATAG_DTB_COMPAT=y
   CONFIG_ARM_ATAG_DTB_COMPAT_CMDLINE_EXTEND=y

2. Build the zImage

   $ ARCH=arm CROSS_COMPILE=... make zImage

3. Build the device tree blobs

   $ ARCH=arm CROSS_COMPILE=... make dtbs

4. Append the correct panda dtb to zImage

   Depending on your hardware it's omap4-panda.dtb, omap4-panda-a4.dtb
   or omap4-panda-es.dtb.

   $ cat arch/arm/boot/zImage arch/arm/boot/dts/omap4-panda-es.dtb > /tmp/appended

5. Use mkimage to produce the appended device tree uImage

   $ mkimage -A arm -O linux -T kernel -C none -a 0x80008000 -e 0x80008000 \
     -n "Linux" -d /tmp/appended /tmp/uImage

Signed-off-by: Tony Lindgren <tony@atomide.com>