i2c:gpio:s5p: I2C GPIO Software implementation (via soft_i2c)

This patch adds support for software I2C for GONI and Universal C210 reference targets.
It adds support for access to GPIOs by number, not as it is present,
by bank and offset.

Signed-off-by: Lukasz Majewski <l.majewski@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>
Cc: Heiko Schocher <hs@denx.de>