i2c:aspeed:support ast2600 i2c new register mode driver

Add i2c new register mode driver to support AST2600 i2c
new register mode. AST2600 i2c controller have legacy and
new register mode. The new register mode have global register
support 4 base clock for scl clock selection, and new clock
divider mode.

Signed-off-by: Ryan Chen <ryan_chen@aspeedtech.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Heiko Schocher <hs@denx.de>