libvpx: bump version to 1.4.0

Use tar.bz2 instead of git.
Also added the hash file.
Changes: https://chromium.googlesource.com/webm/libvpx/+/0080aca235e2d677e49ff46c3e8e77d9dd15858c/CHANGELOG

[Thomas: remove unnecessary LIBVPX_VERSION_MAJOR, as suggested by
Arnout.]

Signed-off-by: Sagaert Johan <sagaert.johan@proximus.be>
Tested-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/libvpx/libvpx.hash

@@ -0,0 +1,2 @@
+# Locally computed:
+sha256  f582d9b2d60a592a4a3d8c32965ca2d2167e9ade38c6c30bac8801ff66a118e4  libvpx-1.4.0.tar.bz2

package/libvpx/libvpx.mk

@@ -4,13 +4,11 @@
 #
 ################################################################################
 
-LIBVPX_VERSION = v1.3.0
-LIBVPX_SITE = http://git.chromium.org/webm/libvpx.git
-LIBVPX_SITE_METHOD = git
-
+LIBVPX_VERSION = 1.4.0
+LIBVPX_SOURCE = libvpx-$(LIBVPX_VERSION).tar.bz2
+LIBVPX_SITE = http://storage.googleapis.com/downloads.webmproject.org/releases/webm
 LIBVPX_LICENSE = BSD-3c
 LIBVPX_LICENSE_FILES = LICENSE PATENTS
-
 LIBVPX_INSTALL_STAGING = YES
 
 # ld is being used with cc options. therefore, pretend ld is cc.