boot: Only do full driver initialization in VMs
    
    Doing the reconnect dance on some real firmware creates huge delays on
    boot. This should not be needed anymore as we now ask the firmware to
    make console devices and xbootldr partitions available explicitly in a
    more targeted fashion.
    
    Fixes: #25510
    (cherry picked from commit f6d59e2ebfc1bf50683a2e640aad501c372a50e4)
    
    Note: I reapplied the original patch by hand, hopefully breaking nothing
    in the process. In 'main' open_volume() was changed to call either
    vmm_open() or open_volume(), and the call to reconnect_all_drivers() was
    moved to vmm_open(). Here, that call is moved to the point where open_volume()
    is called, guarded by is_direct_boot(().