ARM: omap3_logic: Use DEFAULT_LINUX_BOOT_ENV from ti_armv7_common

Since we're including ti_armv7_common, let's pull in DEFAULT_LINUX_BOOT_ENV
and remove unnecessary duplicative definitions.  This patch also renames a
few environmental variables to match what is inside ti_armv7_common. This
should help future-proof any subsequent memory or memory location changes.

Signed-off-by: Adam Ford <aford173@gmail.com>