build: add arch-specific header path to global includes

build: add arch-specific header path to global includes

The global include path, which is used by anything built before EAL,
points to the EAL header files so they utility macros etc. can be used
anywhere in DPDK. This path included the OS-specific EAL header files,
but not the architecture-specific ones. This patch moves the selection
of target architecture to the top-level meson.build file so that the
global include can reference that.

Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
Reviewed-by: Keith Wiles <keith.wiles@intel.com>