nios2: zap nios2-generic board dir

As we use device tree to control u-boot now, the generic
board can be removed.

Signed-off-by: Thomas Chou <thomas@wytron.com.tw>
diff --git a/arch/nios2/Kconfig b/arch/nios2/Kconfig
index 8ae7f6e..bb4fb2a 100644
--- a/arch/nios2/Kconfig
+++ b/arch/nios2/Kconfig
@@ -4,15 +4,11 @@
 config SYS_ARCH
 	default "nios2"
 
-choice
-	prompt "Target select"
-	optional
-
-config TARGET_NIOS2_GENERIC
-	bool "Support nios2-generic"
-
-endchoice
-
-source "board/altera/nios2-generic/Kconfig"
+config SYS_CONFIG_NAME
+	string "Board header file"
+	help
+	  This option should contain the base name of board header file.
+	  The header file include/configs/<CONFIG_SYS_CONFIG_NAME>.h
+	  should be included from include/config.h.
 
 endmenu