tProcv2 tweak, bugfix

[meeg]

• The schedule time for timed instructions (pulse, trigger, send_readoutconfig) can be specified either by writing them to the special time register (s14) before executing the timed instruction, or by including an immediate value in the timed instruction. We were always using the former (because that's fully general, and the latter was not added to the tProc until later), but if the time isn't swept this means using two instructions where only one is really needed. Now we check whether an immediate value can be used.
• The readback check added in changes to improve multiboard sync #342 to tProc v2 load_mem() had a bug which broke things for dmem. Fixed.