serial: Add Goldfish TTY driver

serial: Add Goldfish TTY driver

Add support for the Google Goldfish TTY serial device. This virtual
device is commonly used in QEMU virtual machines (such as the m68k
virt machine) and Android emulators.

The driver implements basic console output and input polling using the
Goldfish MMIO interface.

Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
Reviewed-by: Yao Zi <me@ziyao.cc>
Tested-by: Daniel Palmer <daniel@0x0f.com>
Acked-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Simon Glass <simon.glass@canonical.com>
Acked-by: Angelo Dureghello <angelo@kernel-space.org>