Make XENFIRMWAREDIR a subdir of libexecdir

Put the firmware files below libexecdir. This is essentially just a new
name for the existing path. It has the benefit that it can be configured
via --libexecdir= if required.

Signed-off-by: Olaf Hering <olaf@aepfle.de>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Cc: Ian Campbell <ian.campbell@citrix.com>
Cc: Ian Jackson <ian.jackson@eu.citrix.com>
Cc: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Cc: Wei Liu <wei.liu2@citrix.com>
[ ijc -- ran autogen.sh as requested ]

configure

@@ -600,7 +600,6 @@ XEN_SCRIPT_DIR
 XEN_CONFIG_DIR
 INITD_DIR
 CONFIG_DIR
-XENFIRMWAREDIR
 SHAREDIR
 XEN_LIB_STORED
 XEN_LOG_DIR
@@ -1943,9 +1942,6 @@ XEN_LIB_STORED=$localstatedir/lib/xenstored
 SHAREDIR=$prefix/share
 
 
-XENFIRMWAREDIR=$prefix/lib/xen/boot
-
-
 CONFIG_DIR=$sysconfdir