RK3308B is a enhanced variant of RK3308 with more flexible
iomux and peripherals(for example, RK3308B has 12 pwms, but
RK3308 has 4).
The CHIP_ID is stored in GRF_CHIP_ID:
RK3308: 0xcea (3306 in decimal)
RK3308B: 0x3308
Change-Id: I8f675656c012bdedb43043f5dbeea8bd11ea4ded
Signed-off-by: Andy Yan <andy.yan@rock-chips.com>