qt4: split out SQL driver config flags to QT_SQL_DRIVER_FLAGS

This allows meta-oe to override these options easily in order to enable more
SQL driver plugins.

(From OE-Core rev: 7f12a24771bca786095f823aeb2d322c52c266d2)

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-qt/qt4/qt4.inc

@@ -9,11 +9,13 @@ QT_ENDIAN = "${@qt_endian(d)}"
 QT_DISTRO_FLAGS ?= "-no-accessibility -no-sm"
 QT_DISTRO_FLAGS_linuxstdbase = "-sm"
 
+QT_SQL_DRIVER_FLAGS ?= "-no-sql-ibase -no-sql-mysql -no-sql-psql -no-sql-odbc -plugin-sql-sqlite"
+
 QT_CONFIG_FLAGS += "-release -no-cups -reduce-relocations \
                     -shared -no-nas-sound -no-nis \
                     -qt-gif -system-libjpeg -system-libpng -system-zlib \
-                    -no-sql-ibase -no-sql-mysql -no-sql-psql -no-sql-odbc -plugin-sql-sqlite \
                     -no-pch -qdbus -stl -glib -phonon -webkit \
+                    ${QT_SQL_DRIVER_FLAGS} \
                     ${QT_DISTRO_FLAGS} "
 
 EXTRA_OEMAKE = "-e"