Build: Remove CONFIG_ENABLE_NS_UART_TX_RX_CONTROL

Remove CONFIG_ENABLE_NS_UART_TX_RX_CONTROL CMake variable
as it is not needed after the UART_TX_RX_CONTROL_ENABLED
compile definition was removed from TF-M by a7aa71a.

Signed-off-by: David Vincze <david.vincze@arm.com>
Change-Id: I566e69cbf20eb5fd08f8398944511fb80cf95181
1 file changed