__HAVE_ARCH_GENERIC_BOARD controls availabilty of generic board

We are introducing a new unified board setup. Add a check to make sure that
board config files do not define CONFIG_SYS_GENERIC_BOARD unless their
architecture defines __HAVE_ARCH_GENERIC_BOARD

__HAVE_ARCH_GENERIC_BOARD will currently not be the default setting, but
we can switch this later when most architecture support generic board.

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

README

@@ -3212,6 +3212,16 @@ Configuration Settings:
 	If defined, don't allow the -f switch to env set override variable
 	access flags.
 
+- CONFIG_SYS_GENERIC_BOARD
+	This selects the architecture-generic board system instead of the
+	architecture-specific board files. It is intended to move boards
+	to this new framework over time. Defining this will disable the
+	arch/foo/lib/board.c file and use common/board_f.c and
+	common/board_r.c instead. To use this option your architecture
+	must support it (i.e. must define __HAVE_ARCH_GENERIC_BOARD in
+	its config.mk file). If you find problems enabling this option on
+	your board please report the problem and send patches!
+
 The following definitions that deal with the placement and management
 of environment data (variable area); in general, we support the
 following configurations:

config.mk

@@ -221,6 +221,14 @@ ifeq ($(CONFIG_SPL_BUILD),y)
 CPPFLAGS += -DCONFIG_SPL_BUILD
 endif
 
+# Does this architecture support generic board init?
+ifeq ($(__HAVE_ARCH_GENERIC_BOARD),)
+ifneq ($(CONFIG_SYS_GENERIC_BOARD),)
+$(error Your architecture does not support generic board. Please undefined \
+CONFIG_SYS_GENERIC_BOARD in your board config file)
+endif
+endif
+
 ifneq ($(RESET_VECTOR_ADDRESS),)
 CPPFLAGS += -DRESET_VECTOR_ADDRESS=$(RESET_VECTOR_ADDRESS)
 endif