riscv: clk: Add CLINT clock to kendryte clock driver

Another "virtual" clock (in the sense that it isn't configurable). This
could possibly be done as a clock in the device tree, but I think this is a
bit cleaner.

Signed-off-by: Sean Anderson <seanga2@gmail.com>
diff --git a/include/dt-bindings/clock/k210-sysctl.h b/include/dt-bindings/clock/k210-sysctl.h
index 0e3ed3f..fe852bb 100644
--- a/include/dt-bindings/clock/k210-sysctl.h
+++ b/include/dt-bindings/clock/k210-sysctl.h
@@ -55,5 +55,6 @@
 #define K210_CLK_OTP    43
 #define K210_CLK_RTC    44
 #define K210_CLK_ACLK   45
+#define K210_CLK_CLINT  46
 
 #endif /* CLOCK_K210_SYSCTL_H */