omap: zoom: rename zoom2 name to generic zoom

Replace zoom2 with zoom name in board-zoom-peripherals.c file
This file has functions reused for boards: Zoom2/Zoom3/sdp3630.
Hence have all functions commonly named as zoom

Signed-off-by: Vikram Pandita <vikram.pandita@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>