spl: dm: Kconfig: introduce TPL_RAM (in analogy to SPL_RAM)

To allow finer grained selection of features for TPL, we introduce
TPL_RAM (in analogy to SPL_RAM).

Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>