arm64: dts: ti: k3-am62d2-evm: Remove unused ospi0 chip select pins

arm64: dts: ti: k3-am62d2-evm: Remove unused ospi0 chip select pins

Since only a single flash device is connected to ospi0 retain only the
OSPI0_CSn0 pin configuration and remove the unused CSn1-CSn3 pins from
the default pinctrl. This simplifies the ospi0 pin configuration without
affecting functionality.

Signed-off-by: Paresh Bhagat <p-bhagat@ti.com>
Reviewed-by: Andrew Davis <afd@ti.com>
Link: https://patch.msgid.link/20251029032144.502603-1-p-bhagat@ti.com
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>