arm: mvebu: armada-3720: remove unused config option

The config option CONFIG_DEBUG_UART_CLOCK is not used by Armada 3720's
serial driver (it wasn't even before the recent update of that driver).

Even if it was used, the value was incorrect (the frequency of the clock
is 25 MHz, not 25.8048 MHz).

Remove it from config files and set the default value to 0.

Signed-off-by: Marek Behún <marek.behun@nic.cz>
Cc: Stefan Roese <sr@denx.de>
Cc: Pali Rohár <pali@kernel.org>
Reviewed-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Stefan Roese <sr@denx.de>
diff --git a/configs/mvebu_db-88f3720_defconfig b/configs/mvebu_db-88f3720_defconfig
index c9935da..ff4668e 100644
--- a/configs/mvebu_db-88f3720_defconfig
+++ b/configs/mvebu_db-88f3720_defconfig
@@ -11,7 +11,6 @@
 CONFIG_DM_GPIO=y
 CONFIG_DEFAULT_DEVICE_TREE="armada-3720-db"
 CONFIG_DEBUG_UART_BASE=0xd0012000
-CONFIG_DEBUG_UART_CLOCK=25804800
 CONFIG_DEBUG_UART=y
 CONFIG_AHCI=y
 CONFIG_DISTRO_DEFAULTS=y
diff --git a/configs/mvebu_espressobin-88f3720_defconfig b/configs/mvebu_espressobin-88f3720_defconfig
index 157a4b7..dc199cf 100644
--- a/configs/mvebu_espressobin-88f3720_defconfig
+++ b/configs/mvebu_espressobin-88f3720_defconfig
@@ -11,7 +11,6 @@
 CONFIG_DM_GPIO=y
 CONFIG_DEFAULT_DEVICE_TREE="armada-3720-espressobin"
 CONFIG_DEBUG_UART_BASE=0xd0012000
-CONFIG_DEBUG_UART_CLOCK=25804800
 CONFIG_DEBUG_UART=y
 CONFIG_AHCI=y
 CONFIG_DISTRO_DEFAULTS=y
diff --git a/configs/turris_mox_defconfig b/configs/turris_mox_defconfig
index 34127dc..fd5b6f3 100644
--- a/configs/turris_mox_defconfig
+++ b/configs/turris_mox_defconfig
@@ -11,7 +11,6 @@
 CONFIG_DM_GPIO=y
 CONFIG_DEFAULT_DEVICE_TREE="armada-3720-turris-mox"
 CONFIG_DEBUG_UART_BASE=0xd0012000
-CONFIG_DEBUG_UART_CLOCK=25804800
 CONFIG_DEBUG_UART=y
 CONFIG_OF_BOARD_FIXUP=y
 CONFIG_DISTRO_DEFAULTS=y
diff --git a/configs/uDPU_defconfig b/configs/uDPU_defconfig
index cdf6b22..649248d 100644
--- a/configs/uDPU_defconfig
+++ b/configs/uDPU_defconfig
@@ -10,7 +10,6 @@
 CONFIG_DM_GPIO=y
 CONFIG_DEFAULT_DEVICE_TREE="armada-3720-uDPU"
 CONFIG_DEBUG_UART_BASE=0xd0012000
-CONFIG_DEBUG_UART_CLOCK=25804800
 CONFIG_DEBUG_UART=y
 CONFIG_AHCI=y
 CONFIG_DISTRO_DEFAULTS=y
diff --git a/drivers/serial/Kconfig b/drivers/serial/Kconfig
index 961e3fb..93348c0 100644
--- a/drivers/serial/Kconfig
+++ b/drivers/serial/Kconfig
@@ -443,6 +443,7 @@
 	int "UART input clock"
 	depends on DEBUG_UART
 	default 0 if DEBUG_UART_SANDBOX
+	default 0 if DEBUG_MVEBU_A3700_UART
 	help
 	  The UART input clock determines the speed of the internal UART
 	  circuitry. The baud rate is derived from this by dividing the input