routerstationpro: strip the output kernel of .comment section

The routerstationpro has a 16mb flash which the kernel image should
fit into.  The default build type for vmlinux then should be a
stripped vmlinux.

Use KERNEL_IMAGE_STRIP_EXTRA_SECTIONS  to do this.

Reverts commit 9cd3816e4db97c8fd093a120a75a2b5d193afcdd, which causes:
RedBoot> load -v vlm-boards/19256/kernel
Using default protocol (TFTP)
Unrecognized image type: 0x0

[YOCTO 3515]
[YOCTO 4220]

(From meta-yocto rev: 832f94f9de9c7745256935a522044d37d30794aa)

Signed-off-by: Bruce Ashfield <bruce.ashfield@windriver.com>
Signed-off-by: Michel Thebeau <michel.thebeau@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta-yocto-bsp/conf/machine/routerstationpro.conf

@@ -6,8 +6,9 @@ require conf/machine/include/tune-mips32.inc
 
 MACHINE_FEATURES = "screen keyboard pci usbhost ext2 ext3 serial"
 
-KERNEL_ALT_IMAGETYPE = "vmlinux"
-KERNEL_IMAGETYPE = "vmlinux.bin"
+KERNEL_IMAGETYPE = "vmlinux"
+KERNEL_ALT_IMAGETYPE = "vmlinux.bin"
+KERNEL_IMAGE_STRIP_EXTRA_SECTIONS  = ".comment"
 
 PREFERRED_PROVIDER_virtual/kernel ?= "linux-yocto"
 PREFERRED_VERSION_linux-yocto ?= "3.4%"