clk: at91: add I2S clock mux driver

This driver is a simple muxing driver that controls the
I2S's clock input by using syscon/regmap to change the parent.
The available inputs can be peripheral clock and generated clock.

Signed-off-by: Codrin Ciubotariu <codrin.ciubotariu@microchip.com>
[sboyd@kernel.org: Fix SPDX tag comment style]
Signed-off-by: Stephen Boyd <sboyd@kernel.org>

arch/arm/mach-at91/Kconfig

@@ -27,6 +27,7 @@ config SOC_SAMA5D2
 	select HAVE_AT91_H32MX
 	select HAVE_AT91_GENERATED_CLK
 	select HAVE_AT91_AUDIO_PLL
+	select HAVE_AT91_I2S_MUX_CLK
 	select PINCTRL_AT91PIO4
 	help
 	  Select this if ou are using one of Microchip's SAMA5D2 family SoC.
@@ -129,6 +130,9 @@ config HAVE_AT91_GENERATED_CLK
 config HAVE_AT91_AUDIO_PLL
 	bool
 
+config HAVE_AT91_I2S_MUX_CLK
+	bool
+
 config SOC_SAM_V4_V5
 	bool