Pass up fault codes from various routines, so their callers
can clean up after failures, and remove the FIXME comments
highlighting those previously goofy code paths.

 dap_ap_{read,write}_reg_u32()
 dap_ap_write_reg()
 mem_ap_{read,write}_u32()
 mem_ap_{read,write}_atomic_u32()
 dap_setup_accessport()

Make dap_ap_write_reg_u32() just wrap dap_ap_write_reg(),
instead of cloning its core code (and broken fault handling).

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>