kernel: set default values for ARM low level debugging symbols

kernel: set default values for ARM low level debugging symbols

Set default values for KERNEL_DEBUG_LL and KERNEL_DEBUG_LL_UART_NONE again
as both of these symbols are non visible if KERNEL_EARLY_PRINTK is not
selected and KConfig wont write their value to .config.

This usually is the intended behaviour, but in OpenWrt we are relying on
the KConfig to set these and disable the debug console settings that
multiple targets like mvebu have set in their kernel config.
This was the behaviour before removing all of the "default n" settings
as KConfig by default considers symbols disabled but they are not visible
anymore and thus their value is not set in .config and build system then
later does not override the values from target kernel config.

So, to restore the behaviour to the previous one lets a default value for
KERNEL_DEBUG_LL and KERNEL_DEBUG_LL_UART_NONE.

Fixes: 8bc72ea7be39 ("treewide: strip useless default n Kconfig lines")
Tested-by: Georgi Valkov <gvalkov@gmail.com>
Signed-off-by: Robert Marko <robimarko@gmail.com>