mem: fix 32-bit init config with meson

When building with meson, the default size of virtual address space
reserved for mapping pages was globally set at 512GB, which is too big for
use in 32-bit processes. To match the behaviour with "make", we configure
this to be 512GB for 64-bit and 2GB for 32-bit builds.

Bugzilla ID: 498
Fixes: 66cc45e293ed ("mem: replace memseg with memseg lists")
Cc: stable@dpdk.org
Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
Tested-by: Ferruh Yigit <ferruh.yigit@intel.com>