kprintf should not really care about the hardware-specific details of
each UART or serial port out there, so instead of using x86 specific
instructions, let's ensure that we will compile only the relevant code
for debug output for a targeted-specific platform.
This makes sure that the debug message are properly aligned when running
the kernel bare-metal on a Raspberry Pi. While we are here, also move
the function out of line.
For an upcoming change to support interrupts in this driver, this class
has to inherit from IRQHandler. That in turn will make this class
virtual, which will then actually call the destructor of the class. We
don't want this to happen, thus we have to wrap the class in a
AK::NeverDestroyed.
Previously in the aarch64 Kernel, this would cause dbgln() to actually
print more characters of the next string in memory, because strings in
the Kernel are not zero terminated by default. Prevent this by using the
passed in length of the string.
