eth: fbnic: Use FIELD_PREP to generate minimum firmware version

Create a new macro based on FIELD_PREP to generate easily readable minimum
firmware version ints. This macro will prevent the mistake from the
previous patch from happening again.

Signed-off-by: Lee Trager <lee@trager.us>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Link: https://patch.msgid.link/20250702192207.697368-3-lee@trager.us


Signed-off-by: Jakub Kicinski <kuba@kernel.org>