ARM: zynq: Switch from earlyprintk to earlycon

Switch to earlycon which is preffered over earlyprintk.
It is also sync with Linux kernel (zynq-microzed).

Signed-off-by: Michal Simek <michal.simek@amd.com>
Link: https://lore.kernel.org/r/d280fa18068f80412cf12c235c5245651e7062e2.1679987839.git.michal.simek@amd.com