generic-board: move __HAVE_ARCH_GENERIC_BOARD to Kconfig

Move the option to Kconfig renaming it to CONFIG_HAVE_GENERIC_BOARD.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Alexey Brodkin <abrodkin@synopsys.com>
diff --git a/doc/README.generic-board b/doc/README.generic-board
index 37c1b03..bd8eae1 100644
--- a/doc/README.generic-board
+++ b/doc/README.generic-board
@@ -44,16 +44,18 @@
 
    arc
    arm
+   avr32
+   blackfin
+   m68k
+   microblaze
    mips
+   nios2
    powerpc
    sandbox
    x86
 
-If your architecture is not supported, you need to adjust your
-arch/<arch>/config.mk file to include:
-
-   __HAVE_ARCH_GENERIC_BOARD := y
-
+If your architecture is not supported, you need to select
+HAVE_GENERIC_BOARD in arch/Kconfig
 and test it with a suitable board, as follows.