ARM: EXYNOS: use four additional chipid bits to identify EXYNOS family

Use chipid[27:20] bits to identify the EXYNOS family while setting
up the serial port during the uncompression setup. This uses four
additional bits of chipid to identify the EXYNOS family since this
is required for identifying EXYNOS5420 SoC.

Signed-off-by: Chander Kashyap <chander.kashyap@linaro.org>
Signed-off-by: Thomas Abraham <thomas.abraham@linaro.org>
Reviewed-by: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>