PCI: exynos: Split into Synopsys part and Exynos part

Exynos PCIe IP consists of Synopsys specific part and Exynos
specific part. Only core block is a Synopsys Designware part;
other parts are Exynos specific.

Also, the Synopsys Designware part can be shared with other
platforms; thus, it can be split two parts such as Synopsys
Designware part and Exynos specific part.

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: Pratyush Anand <pratyush.anand@st.com>
Cc: Mohit KUMAR <Mohit.KUMAR@st.com>