usb: ehci: exynos: Fix multiple FDT decode

With current FDT support driver tries to parse device node
twice in ehci_hcd_init() and ehci_hcd_stop(), which shouldn't
happen ideally.
Making provision to store data in a global structure and thereby
passing its pointer when needed.

Signed-off-by: Vivek Gautam <gautam.vivek@samsung.com>