dts: pcm052: bk4: Use proper compatible for QSPI SPI-NOR memory

dts: pcm052: bk4: Use proper compatible for QSPI SPI-NOR memory

In the contemporary U-Boot the "spi-flash" compatible is used only when
CONFIG_$(PHASE_)SPI_FLASH_TINY is defined so spi-nor-tiny.c is compiled.

As vf610 devices are not using SPL at all, the SPI_FLASH_TINY is not
defined and no QSPI flash child nodes are considered as valid ones.

The result is that the 'sf probe' command fails and SPI NOR memory is not
accessible on e.g. BK4 device.

The fix is to use proper compatible - in this case "jedec,spi-nor".

Signed-off-by: Lukasz Majewski <lukma@denx.de>