Having an EFI_RNG_PROTOCOL without a backing RNG device leads to failure
to boot Linux 5.8.
Only install the EFI_RNG_PROTOCOL if we have a RNG device.
Reported-by: Scott K Logan <logans@cottsay.net>
Cc: Neil Armstrong <narmstrong@baylibre.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>