drivers: pcie_ep: iproc: shorten file names

File names such as pcie_ep_bcm_iproc.c / pcie_ep_bcm_iproc_regs.h
seem unnecessarily long, same with CONFIG symbols' names.
Let's shorten them by replacing 'bcm_iproc' with simply 'iproc'.

Signed-off-by: Abhishek Shah <abhishek.shah@broadcom.com>