efi_memory: rename variable to highlight overlap with free memory

efi_memory: rename variable to highlight overlap with free memory

The variable overlap_only_ram is used to specify that the new memory
region that is being created needs to come from the free memory pool
-- this is done by carving out the memory region from the free
memory. The name is a bit confusing though, as other allocated memory
regions, like boot-services code and data are also part of the RAM
memory. Rename the variable to overlap_conventional to highlight the
fact that it is the free/conventional memory that is being referred to
in this context.

Signed-off-by: Sughosh Ganu <sughosh.ganu@linaro.org>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Reviewed-by: Simon Glass <sjg@chromium.org>