uboot: add option to optionally depend on host-openssl

Some U-Boot board configurations have CONFIG_FIT_SIGNATURE=y. In this
case, when U-Boot builds its tools, it requires OpenSSL support on the
host system.

Since we clearly don't want to unconditionally depend on host-openssl,
we introduce a new option to explicitly enable the dependency on
host-openssl. This is exactly identical to the existing
BR2_TARGET_UBOOT_NEEDS_DTC, for the dependency on host-dtc. It is
therefore the responsibility of the user to enable this option if his
board configuration uses CONFIG_FIT_SIGNATURE=y.

Necessary to fix bug #9316.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

boot/uboot/Config.in

@@ -137,6 +137,14 @@ config BR2_TARGET_UBOOT_NEEDS_DTC
 	  Select this option if your U-Boot board configuration
 	  requires the Device Tree compiler to be available.
 
+config BR2_TARGET_UBOOT_NEEDS_OPENSSL
+	bool "U-Boot needs OpenSSL"
+	help
+	  Select this option if your U-Boot board configuration
+	  requires OpenSSL to be available on the host. This is
+	  typically the case when the board configuration has
+	  CONFIG_FIT_SIGNATURE enabled.
+
 menu "U-Boot binary format"
 
 config BR2_TARGET_UBOOT_FORMAT_AIS

boot/uboot/uboot.mk

@@ -133,6 +133,10 @@ ifeq ($(BR2_TARGET_UBOOT_NEEDS_DTC),y)
 UBOOT_DEPENDENCIES += host-dtc
 endif
 
+ifeq ($(BR2_TARGET_UBOOT_NEEDS_OPENSSL),y)
+UBOOT_DEPENDENCIES += host-openssl
+endif
+
 # prior to u-boot 2013.10 the license info was in COPYING. Copy it so
 # legal-info finds it
 define UBOOT_COPY_OLD_LICENSE_FILE