omap: zoom2: split board file for software reuse

Split zoom2 board file into:
base board file and a board-zoom-peripherals.c file

that way the same peripherals file can be reused for: zoom3 and sdp3630

Following list shows the commonality across the three platforms and hence the
case for software reuse:

Peripheral    zoom2    zoom3  sdp3630
---------------------------------------
Ethernet        smsc    smsc    smc
NOR             n/a     n/a     B
Onenand         n/a     n/a     B
HDMI            A       A       B (present on different i2c)
NAND            A       A       A (same nand)
SDRAM           A       A       A (same sdram)
Keypad          A       A       A (same twl)
Camera          A       A       A (same sensor can be mounted)
LCD Display     A       A       A (same wvga display)
OPPs            A       A       A (same chip feature)
Audio           A       A       A (same audio via twl5030)

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