arm: dts: socfpga: Fix SPI aliases

arm: dts: socfpga: Fix SPI aliases

The SPI aliases are completely wrong. First, they point to non-existing
/spi@.* nodes instead of the correct /soc/spi@.* nodes. Second, the use
ad-hoc string instead of a handle. Furthermore, they are copied multiple
times in each board DTS.

So fix it such that we move these into socfpga.dtsi and make them use
the usual handles.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Dinh Nguyen <dinguyen@opensource.altera.com>