OMAP1: Fix non-working LCD on OMAP310

This patch fixes bug introduced in revision:

f8e9e984
omap1: DMA: move LCD related code from plat-omap to mach-omap1

The code introduced by this patch didn't consider any other CPUs but OMAP1510,
which rendered OMAP310 -- which has the same LCD controller -- non-working. Use
cpu_is_omap15xx() instead of cpu_is_omap1510() to squash this issue.

Bug found on Palm Zire 71 hardware.

Signed-off-by: Marek Vasut <marek.vasut@gmail.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>