[U-Boot] Proper CONFIG_SPL_TEXT_BASE value for OMAP3

[Adam Ford]

ti_omap3_common.h defines CONFIG_SPL_TEXT_BASE to 0x40200800, however
a significant number of omap3 boards un-define this and redefine it to
0x40200000

Is there any reason, we couldn't just make ti_omap3_common.h define
CONFIG_SPL_TEXT_BASE to 0x40200000?  (or better yet migrate to Kconfig
and make 0x40200000 the default)?

Boarding using 0x40200800 (default)

cm_t35.h
am3517_crane.h
tao3530.h

Board using 0x40200000:
omap3_logic.h
tricorder.h
omap3_evm.h
tam3517-common.h
omap3_beagle.h
omap3_overo.h
sniper.h
omap3_igep00x0.h
devkit8000.h
include/configs/am3517_evm.h

If we do that, we can limit the number of undefs and redefines and
clean up the headers a bit.

adam