boot/at91bootstrap: add legal information

The old at91bootstrap version (1.x) uses a strange variant of the BSD
license, called "BSD Source Code Attribution" and referenced by SPDX
as BSD-Source-Code.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
(cherry picked from commit 3887e8c095106762173b13127deb9c7da68c0625)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

boot/at91bootstrap/at91bootstrap.hash

@@ -1,2 +1,3 @@
 # locally computed
 sha256  d66192a274247f4baa39fa932eadf903d7add55641d89d30402f967c4f2282a5  AT91Bootstrap1.16.zip
+sha256  6a3ac5dfcf19e6bac1b1109d30d72818768a3855e2594b84fe2b012b5fe0e77b  include/sdramc.h

boot/at91bootstrap/at91bootstrap.mk

@@ -7,6 +7,8 @@
 AT91BOOTSTRAP_VERSION = 1.16
 AT91BOOTSTRAP_SITE = ftp://www.at91.com/pub/at91bootstrap
 AT91BOOTSTRAP_SOURCE = AT91Bootstrap$(AT91BOOTSTRAP_VERSION).zip
+AT91BOOTSTRAP_LICENSE = BSD-Source-Code
+AT91BOOTSTRAP_LICENSE_FILES = include/sdramc.h
 
 AT91BOOTSTRAP_BOARD = $(call qstrip,$(BR2_TARGET_AT91BOOTSTRAP_BOARD))
 AT91BOOTSTRAP_MEMORY = $(call qstrip,$(BR2_TARGET_AT91BOOTSTRAP_MEMORY))