loader: Add AddressSpace loading support to ELFs

loader: Add AddressSpace loading support to ELFs

Add a new function load_elf_as() that allows the caller to specify an
AddressSpace to use when loading the ELF. The original load_elf()
function doesn't have any change in functionality.

Signed-off-by: Alistair Francis <alistair.francis@xilinx.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 8b5cefecdf56fba4ccdff2db880f0b6b264cf16f.1474331683.git.alistair.francis@xilinx.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>