lava: Extend timeouts due to Minnowboard memory cleaning issue

Minnowboard currently get stuck for a few minutes during boot with this message:

Clear memory in MRC per MOR request Start, Please wait for some minutes...

This indicates that the firmware is busy overwriting (slowly) the RAM contents. This is triggered by the CONFIG_RESET_ATTACK_MITIGATION kernel option, enabled by default in Debian kernels, setting the MemoryOverwriteRequestControl/MemoryOverwriteRequestControlLock UEFI variables.

A request to drop the kernel option has been submitted upstream: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=970861

Further details about the UEFI variables and their behaviour in the EDK2 TianoCore firmware here:

https://edk2.groups.io/g/discuss/topic/77180459#381

The memory cleaning process seems to be largely outside of the control of the free firmware, so the suggested option is to avoid triggering it from the OS kernel. The best way to do so is still unclear and should be discussed in the above Debian bug. In the meantime, increase the timeouts.

See also APERTIS-7296 for further details.