default or selected kernelversion does not have config value CONFIG_UART3_CTS_PIN.
Result is shown for kernelversion 5.4.69
UART3 CTS pin
configname: CONFIG_UART3_CTS_PIN
Linux Kernel Configuration
└─>Device Drivers
└─>Character devices
└─>Serial drivers
└─>UART3 CTS pin
In linux kernel since version 2.6.30 (release Date: 2009-06-09)
Refer to arch/blackfin/mach-*/include/mach/gpio.h to see the GPIO map.