routerstationpro: swap KERNEL_IMAGETYPE and KERNEL_ALT_IMAGETYPE

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

Swapping KERNEL_IMAGETYPE and KERNEL_ALT_IMAGETYPE for rsp causes
vmlinux.bin to be linked in tmp/deploy/images instead of vmlinux, and
causes vmlinux.bin to appear in the kernel rpm file.

[YOCTO #3515]

(From meta-yocto rev: 70b569e9ea92a680f23b9bfddb2f27f4f5df3028)

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