hifive1: Add RENODE_UART variable to board.cmake

Set RENODE_UART variable describing which UART device
should be used when running Robot Framework test on the platform.

Signed-off-by: Michał Szprejda <mszprejda@antmicro.com>
Signed-off-by: Mateusz Hołenko <mholenko@antmicro.com>
diff --git a/boards/riscv/hifive1/board.cmake b/boards/riscv/hifive1/board.cmake
index 212dd82..8d5f847 100644
--- a/boards/riscv/hifive1/board.cmake
+++ b/boards/riscv/hifive1/board.cmake
@@ -2,6 +2,7 @@
 
 set(SUPPORTED_EMU_PLATFORMS renode qemu)
 set(RENODE_SCRIPT ${CMAKE_CURRENT_LIST_DIR}/support/hifive1.resc)
+set(RENODE_UART sysbus.uart0)
 
 set(QEMU_binary_suffix riscv32)
 set(QEMU_CPU_TYPE_${ARCH} riscv32)