arm: omap3: Make try_unlock_memory() static

try_unlock_memory() is only used in one file, so make it static
in that file,remove it from the sys_proto header file, and relocate
it into the #ifdef section that call it. This will make it only built
under the conditions when it is called, and it may help with some
further optimization in the future.

Signed-off-by: Adam Ford <aford173@gmail.com>
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Link: https://lore.kernel.org/r/20210625192308.277136-2-aford173@gmail.com