arm: Disable ATAGs support

With the exceptions of ds109, ds414, icnova-a20-swac, nokia_rx51 and
stemmy, disable ATAG support.  A large number of platforms had enabled
support but never supported a kernel so old as to require it.  Further,
some platforms are old enough to support both, but are well supported by
devicetree booting, and have been for a number of years.  This is
because some of the ATAGs related functions have been re-used to provide
the same kind of information, but for devicetree or just generally to
inform the user.  When needed still, rename these functions to
get_board_revision() instead, to avoid conflicts.  In other cases, these
functions were simply unused, so drop them.

Cc: Andre Przywara <andre.przywara@arm.com>
Cc: Jagan Teki <jagan@amarulasolutions.com>
Cc: Phil Sutter <phil@nwl.cc>
Cc: Stefan Bosch <stefan_b@posteo.net>
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/board/Synology/common/Makefile b/board/Synology/common/Makefile
index 62354cc..f688b54 100644
--- a/board/Synology/common/Makefile
+++ b/board/Synology/common/Makefile
@@ -2,4 +2,4 @@
 #
 # Copyright (C) 2021 Phil Sutter <phil@nwl.cc>
 
-obj-y	+= legacy.o
+obj-$(SUPPORT_PASSING_ATAGS)	+= legacy.o