po: Fix Makefile rules for in-tree builds without configuration

po: Fix Makefile rules for in-tree builds without configuration

Adding 'update' to the phony targets fixes this error:

$ LANG=C make -C po update
make: Entering directory `/qemu/po'
  LINK  update
/qemu/po/de_DE.po: file not recognized: File format not recognized
collect2: error: ld returned 1 exit status
make: *** [update] Error 1
make: Leaving directory `/qemu/po'

Some other phony targets (build, install) were also added, and the
existing .PHONY statement was moved to a more prominent position at
the beginning of the Makefile.

The patch also fixes a 2nd bug. The default target should be 'all',
but instead 'modules' (from rules.mak) was the default. Fix this by
adding 'all' as a target before any include statement.

Signed-off-by: Stefan Weil <sw@weilnetz.de>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>