ARM: dts: nspire: Fix SP804 users

Even though the SP804 binding allows to specify only one clock, the
primecell driver requires a named clock to activate the bus clock.

Specify the one clock three times and provide some clock-names, to
make the DT match the SP804 and primecell binding.

Link: https://lore.kernel.org/r/20200907121831.242281-3-andre.przywara@arm.com


Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Olof Johansson <olof@lixom.net>