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 <[e-mail]>
Acked-by: Krzysztof Kozlowski <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Stephen Boyd <[e-mail]>

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

···
 #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