lvgl: Update defconfig

Update the defconfig to use Linux default settings. Settings are taken
from the linux.defconfig from the source repository. This includes the
following changes:
- use libc based malloc, string, sprintf. Using libc based memory
  allocation eliminates the risk that the lvgl application runs out of
  memory because of fixed internal memory size.
- use OS based pthread implementation
- set refresh period to 16 ms (60 FPS max)
- increase LV_DRAW_LAYER_SIMPLE_BUF_SIZE and
  CONFIG_LV_DRAW_THREAD_STACK_SIZE

Signed-off-by: Thorsten Schmelzer <t.schmelzer@phytec.de>
Signed-off-by: Khem Raj <khem.raj@oss.qualcomm.com>

meta-oe/recipes-graphics/lvgl/files/defconfig

@@ -1,3 +1,10 @@
+CONFIG_LV_USE_CLIB_MALLOC=y
+CONFIG_LV_USE_CLIB_STRING=y
+CONFIG_LV_USE_CLIB_SPRINTF=y
+CONFIG_LV_OS_PTHREAD=y
 CONFIG_LV_COLOR_DEPTH_32=y
+CONFIG_LV_DEF_REFR_PERIOD=16
+CONFIG_LV_DRAW_LAYER_SIMPLE_BUF_SIZE=262144
+CONFIG_LV_DRAW_THREAD_STACK_SIZE=65536
 # CONFIG_LV_BUILD_EXAMPLES is not set
 # CONFIG_LV_BUILD_DEMOS is not set