soc: xilinx: zynq7000: move to using DT_STRING_UPPER_TOKEN_BY_IDX macro
soc: xilinx: zynq7000: move to using DT_STRING_UPPER_TOKEN_BY_IDX macro

Replaced hand coded use with DT_STRING_UPPER_TOKEN_BY_IDX.  We should have
introduced the APIs when this was needed since the token values in
devicetree_generated.h should only be accessed via an API macro.

Signed-off-by: Kumar Gala <383ef5577c6e1178b93f59ec8d0936f76d2a98c4@kernel.org>

finikorg/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,finikorg/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,finikorg/zephyr,finikorg/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,galak/zephyr