configs: ti: armv7_common: enable Thumb mode for all

Commit bd2c4522

 ("ti: armv7: enable EXT support in SPL (using
ti_armv7_common.h)") enabled thumb mode only for SPL builds, however,
All TI armv7 platforms do support thumb, and there is no reason why the
space savings cannot be exploited for u-boot as well.

Reported-by: Murali Karicheri <m-karicheri2@ti.com>
Suggested-by: Tom Rini <trini@konsulko.com>
Signed-off-by: Nishanth Menon <nm@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>