arm64: dts: socfpga: agilex: Add 4-bit SPI bus width

arm64: dts: socfpga: agilex: Add 4-bit SPI bus width

Add spi-tx-bus-width and spi-rx-bus-width properties with value 4 to the
agilex device tree. This update configures the SPI controller to use a
4-bit bus width for both transmission and reception, potentially improving
SPI throughput and matching the hardware capabilities more closely.

Signed-off-by: Fong, Yan Kei <yan.kei.fong@altera.com>
Reviewed-by: Khairul Anuar Romli <khairul.anuar.romli@altera.com>
Reviewed-by: Matthew Gerlach <matthew.gerlach@altera.com>
Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>