Provide both a 3.0.x and a 3.1 set of headers to the toolchain.
Compatibility is maintained with older 2.6 headers by creating a
new variable that changes the SRC_URI based on the major version
number of the kernel.
Built and booted with 2.6.37.2, 3.0.8 and 3.1 linux-libc-headers.
Signed-off-by: Bruce Ashfield <bruce.ashfield@windriver.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>