build: use configure for watchdog-default-timeout & others

Move arch-checking from code to single point in spec-file.
Instead of using sed to poke around in config-file have
SBD_WATCHDOG_TIMEOUT_DEFAULT, SBD_SYNC_RESOURCE_STARTUP_DEFAULT &
SBD_SYNC_RESOURCE_STARTUP_SYSCONFIG configurable via configure.
! caveat builders: assure that watchdog-timeout-default !
! given to configure is valid for arch !
! (namely s390x doesn't support < 15s) !
! check with example spec-file !