clk: mtmips: add clock driver for MediaTek MT7621 SoC

This patch adds a clock driver for MediaTek MT7621 SoC.
This driver provides clock gate control as well as getting clock frequency
for CPU/SYS/XTAL and some peripherals.

Reviewed-by: Sean Anderson <seanga2@gmail.com>
Signed-off-by: Weijie Gao <weijie.gao@mediatek.com>

include/dt-bindings/clock/mt7621-clk.h

@@ -0,0 +1,46 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2022 MediaTek Inc. All rights reserved.
+ *
+ * Author: Weijie Gao <weijie.gao@mediatek.com>
+ */
+
+#ifndef _DT_BINDINGS_MT7621_CLK_H_
+#define _DT_BINDINGS_MT7621_CLK_H_
+
+#define MT7621_CLK_XTAL		0
+#define MT7621_CLK_CPU		1
+#define MT7621_CLK_BUS		2
+#define MT7621_CLK_50M		3
+#define MT7621_CLK_125M		4
+#define MT7621_CLK_150M		5
+#define MT7621_CLK_250M		6
+#define MT7621_CLK_270M		7
+
+#define MT7621_CLK_HSDMA	8
+#define MT7621_CLK_FE		9
+#define MT7621_CLK_SP_DIVTX	10
+#define MT7621_CLK_TIMER	11
+#define MT7621_CLK_PCM		12
+#define MT7621_CLK_PIO		13
+#define MT7621_CLK_GDMA		14
+#define MT7621_CLK_NAND		15
+#define MT7621_CLK_I2C		16
+#define MT7621_CLK_I2S		17
+#define MT7621_CLK_SPI		18
+#define MT7621_CLK_UART1	19
+#define MT7621_CLK_UART2	20
+#define MT7621_CLK_UART3	21
+#define MT7621_CLK_ETH		22
+#define MT7621_CLK_PCIE0	23
+#define MT7621_CLK_PCIE1	24
+#define MT7621_CLK_PCIE2	25
+#define MT7621_CLK_CRYPTO	26
+#define MT7621_CLK_SHXC		27
+
+#define MT7621_CLK_MAX		28
+
+/* for u-boot only */
+#define MT7621_CLK_DDR		29
+
+#endif /* _DT_BINDINGS_MT7621_CLK_H_ */