[DRIVERS] Use vmm_inb and vmm_outb to access uart

Since on x86 UART is IO mapped, vmm_in_8 et all won't
work on x86. Change the access to vmm_inb which uses
I/O space instructions on x86 and does MMIO on other
architectures.

Signed-off-by: Himanshu Chauhan <hschauhan@nulltrace.org>
[x86] Make serial port as default console.

Make serial port as the default console for x86.
It can be overridden to use STDIO by having
console=stdio in the command line.

Signed-off-by: Himanshu Chauhan <hschauhan@nulltrace.org>
[x86] Fix compilation and Enable 8250 code.

Signed-off-by: Himanshu Chauhan <hschauhan@nulltrace.org>