clk: renesas: cpg-mssr: add generic support for read-only DIV6 clocks

Gen3 has two clocks (OSC and R) which look like a DIV6 clock but their
divider value is read-only and depends on MD pins at bootup. Add support
for such clocks by reading the value and adding a fixed clock.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>

drivers/clk/renesas/renesas-cpg-mssr.h

@@ -37,6 +37,7 @@ enum clk_types {
 	CLK_TYPE_IN,		/* External Clock Input */
 	CLK_TYPE_FF,		/* Fixed Factor Clock */
 	CLK_TYPE_DIV6P1,	/* DIV6 Clock with 1 parent clock */
+	CLK_TYPE_DIV6_RO,	/* DIV6 Clock read only with extra divisor */
 
 	/* Custom definitions start here */
 	CLK_TYPE_CUSTOM,
@@ -53,6 +54,8 @@ enum clk_types {
 	DEF_BASE(_name, _id, CLK_TYPE_FF, _parent, .div = _div, .mult = _mult)
 #define DEF_DIV6P1(_name, _id, _parent, _offset)	\
 	DEF_BASE(_name, _id, CLK_TYPE_DIV6P1, _parent, .offset = _offset)
+#define DEF_DIV6_RO(_name, _id, _parent, _offset, _div)	\
+	DEF_BASE(_name, _id, CLK_TYPE_DIV6_RO, _parent, .offset = _offset, .div = _div, .mult = 1)
 
     /*
      * Definitions of Module Clocks