ARM: OMAP2+: Fix build error after merge

Commit 9890ce44 (ARM: get rid of asm/irq.h in asm/prom.h)
removed include of asm/irq.h in asm/prom.h. This commit
together with recent omap cleanup to remove io.h causes
build breakage:

arrch/arm/mach-omap2/control.c: In function 'omap3_ctrl_write_boot_mode':
arch/arm/mach-omap2/control.c:238: error:
'OMAP343X_CTRL_BASE' undeclared (first use in this function)
...

Fix this by including hardware.h directly where needed
instead of relying on asm/irq.h in asm/prom.h.

Reported-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Tony Lindgren <tony@atomide.com>