Export variable for device sanitize arch to Soong

Also renames the variable from SANITIZE_ARCH to SANITIZE_TARGET_ARCH,
and makes it only apply to the device.

Bug: 29498013
Test: No change to build.ninja files with m -j SANITIZE_TARGET=address
Change-Id: Ib5f6ab448f5d96d2426c983308136670f9a55b7b