arm: socfpga: dts: Add spi0 alias for Cadence QSPI driver

arm: socfpga: dts: Add spi0 alias for Cadence QSPI driver

Without this alias, DM based probing does not work. So lets add this
alias to get the bus numbering correct.

Signed-off-by: Stefan Roese <[email protected]>
Cc: Chin Liang See <[email protected]>
Cc: Dinh Nguyen <[email protected]>
Cc: Vince Bridgers <[email protected]>
Cc: Marek Vasut <[email protected]>
Cc: Pavel Machek <[email protected]>
Cc: Simon Glass <[email protected]>
Cc: Jagannadha Sutradharudu Teki <[email protected]>