doc/develop/spl.rst describes SPL, TPL, VPL.
Remove the outdated README.TPL document.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>

Now that Linux has accepted these tags, move U-Boot over to use them.
Tidy up the comments and formatting, making sure that VPL is mentioned
too.

Signed-off-by: Simon Glass <sjg@chromium.org>

Signed-off-by: Thomas Hebb <tommyhebb@gmail.com>

Add documentation for the pre-reloc property in SPL and TPL device-tree:
- u-boot,dm-pre-proper
- u-boot,dm-pre-reloc
- u-boot,dm-spl
- u-boot,dm-tpl

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

Prior to Kbuild, $(TOPDIR) or $(SRCTREE) was used for
pointing to the top of source directory.
(No difference between the two.)

In Kbuild style, $(srctree) is used instead.
This commit renames TOPDIR to srctree and delete the
defition of TOPDIR.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>

Due to the nand SPL on some board(e.g. P1022DS)has a size limit, it can
not be more than 4K. So, the SPL cannot initialize the DDR with the SPD
code. This patch introduces TPL to enable a loader stub that is loaded
by the code from the SPL. It initializes the DDR with the SPD or other
operations.

The TPL's size is sizeable, the maximum size is decided by the memory's
size that TPL runs. It initializes the DDR through SPD code, and copys
final uboot image to DDR. So there are three stage uboot images:
	* spl_boot, * tpl_boot, * final uboot image

Signed-off-by: Ying Zhang <b40530@freescale.com>
Acked-by: York Sun <yorksun@freescale.com>