ZCU102: Enable HAVE_TIMER tests and fix failing ones

(Moved from https://sel4.atlassian.net/browse/SELFOUR-2272)
The timer tests are failing and are disabled for the zynqmp platform in `settings.cmake` currently.  This appears to be due to using the same timers as the zc706 platform, but without updating the input clk frequencies for the different platform (see also https://github.com/seL4/util_libs/issues/119)