augeas: Add libxml2 dependency

augeas: Add libxml2 dependency

This patch fixes the following Augeas configure error.

| checking for LIBXML... no
| configure: error: Package requirements (libxml-2.0) were not met:
|
| No package 'libxml-2.0' found
|
| Consider adjusting the PKG_CONFIG_PATH environment variable if you
| installed software in a non-standard prefix.
|
| Alternatively, you may set the environment variables LIBXML_CFLAGS
| and LIBXML_LIBS to avoid the need to call pkg-config.
| See the pkg-config man page for more details.
| ERROR: oe_runconf failed

(From OE-Core rev: 72edbba1ad212986be74aaa15eb9c785c6456d30)

Signed-off-by: Martin Donnelly <martin.donnelly@ge.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>