docs/manual: update external toolchain examples

Replace ADI by Analog Devices, which is clearer for most people, and
remove the Xilinx external toolchains since we have deprecated them.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

docs/manual/configure.txt

@@ -138,10 +138,9 @@ http://www.linaro.org[Linaro] for ARM,
 http://www.mentor.com/embedded-software/sourcery-tools/sourcery-codebench/editions/lite-edition/[Sourcery
 CodeBench] for ARM, x86, x86-64, PowerPC, MIPS and SuperH,
 https://blackfin.uclinux.org/gf/project/toolchain[Blackfin toolchains
-from ADI], http://git.xilinx.com/[Xilinx toolchains for Microblaze],
-etc.) and is capable of downloading them automatically, or it can be
-pointed to a custom toolchain, either available for download or
-installed locally.
+from Analog Devices], etc.) and is capable of downloading them
+automatically, or it can be pointed to a custom toolchain, either
+available for download or installed locally.
 
 Then, you have three solutions to use an external toolchain: