webos_qmake5: Remove unneeded code

* drop do_generate_qt_config_file, right config is already created
  by qmake5_base.bbclass
* drop QT_DIR_NAME already set by qmake5_base.bbclass
* drop export QT_CONF_PATH already done by qmake5_base.bbclass
* use EXTRA_QMAKEVARS_PRE to define WEBOS_* variables and
  qmake5_do_configure to respect debug flag and other possible flags

[GF-2010] Fix shared state issues with meta-qt5

Open-webOS-DCO-1.0-Signed-off-by: Martin Jansa <martin.jansa@lge.com>
Change-Id: I5f1eae6f8c13f882e2aeae01563d4f07fbb02655
webos_qmake5: Use OE_QMAKE_PATH_* variables

[GF-2010] Fix shared state issues with meta-qt5

Open-webOS-DCO-1.0-Signed-off-by: Martin Jansa <martin.jansa@lge.com>
Change-Id: I59117e66e1825a65a0a0b8b23fae3f538f03dd78
webos_qmake5: export MACHINE variable from MACHINE_ARCH recipes

* export WEBOS_QMAKE_MACHINE in do_configure
* export WEBOS_QMAKE_TARGET in EXTRA_OEMAKE
* export them only in MACHINE_ARCH recipes (inherit webos_machine_dep)
* a lot of recipes were exporting it in own do_configure
  this way we can check that only MACHINE_ARCH exports it
* recipe can define WEBOS_QMAKE_MACHINE variable, to use differnt
  MACHINE variable for project file and OE
* recipe can define WEBOS_QMAKE_TARGET variable, if it needs MACHINE
  variable defined for make (and again it doesn't need to match OE
  MACHINE)

[GF-2010] Fix shared state issues with meta-qt5

Open-webOS-DCO-1.0-Signed-off-by: Martin Jansa <martin.jansa@lge.com>
Change-Id: I55faf50783601e7855c4bb2fb6bc90b6e67851c3