* Introduce 64-bit tick counter
* Let the timer always count when possible, also if it already fired
* Simplify the kernel syscall API to have one current time call,
which returns the elapsed microseconds since boot
* Acknowledge receive of page-fault signal with ack_signal,
but restart thread execution separately
* use kill_signal_context when disolving a pager_object to prevent race
* Remove bureaucracy in form of Thread_event and Signal_ack_handler
* remove dead code in riscv, namely Thread_base definition
* translation_table_insertions function for ARM drops out,
which was overcautious
This commit adds rocket core on the Zynq FPGA support to base HW. It also takes
advantage of the new timer infrastructure introduced with the privileged 1.8 and
adds improved TLB flush support.
fixes#1880
