dt-bindings: clock: add loongson-2 boot clock index

The Loongson-2 boot clock was used to spi and lio peripheral and
this patch was to add boot clock index number.
Signed-off-by: Yinbo Zhu <zhuyinbo@loongson.cn>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20230323025229.2971-1-zhuyinbo@loongson.cnSigned-off-by: Stephen Boyd <sboyd@kernel.org>

include/dt-bindings/clock/loongson,ls2k-clk.h

@@ -24,6 +24,7 @@
 #define LOONGSON2_SATA_CLK				14
 #define LOONGSON2_PIX0_CLK				15
 #define LOONGSON2_PIX1_CLK				16
-#define LOONGSON2_CLK_END				17
+#define LOONGSON2_BOOT_CLK				17
+#define LOONGSON2_CLK_END				18
 
 #endif