armv7m: Abstract out the "load kernel" code

armv7m: Abstract out the "load kernel" code

Abstract the "load kernel" code out of armv7m_init() into its own
function.  This includes the registration of the CPU reset function,
to parallel how we handle this for A profile cores.

We make the function public so that boards which choose to
directly instantiate an ARMv7M device object can call it.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Alistair Francis <alistair.francis@xilinx.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Message-id: 1487604965-23220-2-git-send-email-peter.maydell@linaro.org