unncecessary

even if the real serial console is not working, keep_bootcon is a better solution
select HAVE_ARM_ARCH_TIMER instead of the raw clocksource ARM_ARCH_TIMER
it seems necessary to enable timer7 for the ARM_ARCH_TIMER to work
remove rk_serial again

Now with arch_timer running correctly, the 8250_dw serial driver is
able to handle the serial console just fine.