A few headers are included twice, remove them.

Found the following errors using make includecheck:
arch/arm/mach-omap2/clock44xx_data.c: prm44xx.h is
included more than once.
arch/arm/mach-omap2/clockdomains44xx_data.c: cm1_44xx.h
is included more than once.
arch/arm/mach-omap2/clockdomains44xx_data.c: cm2_44xx.h
is included more than once.
arch/arm/mach-omap2/powerdomain2xxx_3xxx.c: prm-regbits-34xx.h
is included more than once.

Cc: Paul Walmsley <paul@pwsan.com>
Cc: Tony Lindgren <tony@atomide.com>
Cc: Russell King <linux@arm.linux.org.uk>
Signed-off-by: NFelipe Balbi <balbi@ti.com>
[paul@pwsan.com: dropped lists from patch cc:s; tweaked subject line]
Signed-off-by: NPaul Walmsley <paul@pwsan.com>