firmware: Restore support for built-in firmware

Commit 5620a0d1aac ("firmware: delete in-kernel firmware") removed the
entire firmware directory.  Unfortunately it thereby also removed the
support for built-in firmware.

This restores the ability to build firmware directly into the kernel by
pruning the original Makefile to the necessary minimum.  The default for
EXTRA_FIRMWARE_DIR is now the standard directory /lib/firmware/.

Fixes: 5620a0d1aac ("firmware: delete in-kernel firmware")
Signed-off-by: Markus Trippelsdorf <markus@trippelsdorf.de>
Acked-by: Greg K-H <gregkh@linuxfoundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/drivers/base/Kconfig b/drivers/base/Kconfig
index f046d21..1a5f6a1 100644
--- a/drivers/base/Kconfig
+++ b/drivers/base/Kconfig
@@ -140,13 +140,10 @@
 config EXTRA_FIRMWARE_DIR
 	string "Firmware blobs root directory"
 	depends on EXTRA_FIRMWARE != ""
-	default "firmware"
+	default "/lib/firmware"
 	help
 	  This option controls the directory in which the kernel build system
 	  looks for the firmware files listed in the EXTRA_FIRMWARE option.
-	  The default is firmware/ in the kernel source tree, but by changing
-	  this option you can point it elsewhere, such as /lib/firmware/ or
-	  some other directory containing the firmware files.
 
 config FW_LOADER_USER_HELPER
 	bool