ARM: OMAP1: fix sparse warning added by commit 4c98dc6b

Commit 4c98dc6b

 ("ARM: OMAP: Make
plat/fpga.h local to arch/arm/plat-omap") results in a new warning from
sparse:

arch/arm/mach-omap1/fpga.c:147:6: warning: symbol 'omap1510_fpga_init_irq' was not declared. Should it be static?

Fix by adding a missing include.

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Cc: Tony Lindgren <tony@atomide.com>