timer: Add Goldfish timer driver

timer: Add Goldfish timer driver

Add support for the Goldfish timer driver. This driver utilizes the
Goldfish RTC hardware to provide a nanosecond-resolution timer. This
virtual device is commonly found in QEMU virtual machines (such as the
m68k virt machine) and Android emulators.

The driver implements the standard U-Boot timer UCLASS interface,
exposing a 64-bit monotonically increasing counter with a 1GHz clock
rate derived from the RTC registers.

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