Correct support statements for virtual media firmware

The bare metal IPI documentation section Firmware requirements for installing with virtual media contains the following statement: "The following table lists supported firmware"

It should say "tested firmware" and "known-to-work minimum firmware versions" instead (or known-to-not-work below listed firmware versions). The current wording makes it look like we don't support other firmware, which isn't accurate.

We should add that "we recommend to upgrade the firmware to the latest supported versions by the your hardware vendor" 

The overall logic is that we support Redfish virtual media in general, which is implemented by many vendors in their firmware, and we have identified firmware versions below which we know virtual media doesn't work (listed in the table), but we still support it in general.

Examples If a customer asks:

• When will you support Dell 15th generation? 

We support Redfish virtual media in Dell nodes, we will work on issues related Redfish virtual media.

• My node supports Redfish but this doesn't work.

If an issue has has its root cause in the the implementation of Redfish in the hardware's firmware we may request that the the vendor fix it. If the issue is in the Redfish libraries in OpenShift we will work on the fix.

Please use the above information to amend the documentation to reflect the general support of Redfish virtual media.