[doc] Mark icache verification as "done for now"
[doc] Mark icache verification as "done for now"

The icache verification is complete until new bugs are found, let's mark
it as such in the docs.

AmbiML/ibex,lowRISC/ibex,AmbiML/ibex,lowRISC/ibex,AmbiML/ibex,AmbiML/ibex,lowRISC/ibex,lowRISC/ibex