ARM: omap3: evm: Remove CONFIG_SYS_NS16550_REG_SIZE undefine

This commit removes an attempt to workaround a previous compilation
warning that is is now fixed in "include/configs/ti_omap3_common.h".

Signed-off-by: Derald D. Woods <woods.technical@gmail.com>
Reviewed-by: Tom Rini <trini@konsulko.com>