riscv: dts: thead: remove enabled property for spi0

There are currently no nodes that use spi0 so remove the enabled
property for it in the beaglev ahead and lpi4a dts files. It can be
re-enabled in the future if any peripherals will use it. The definition
of spi0 remains in the th1520.dtsi file.

Suggested-by: Emil Renner Berthing <emil.renner.berthing@canonical.com>
Signed-off-by: Drew Fustini <dfustini@tenstorrent.com>