BBB+Android 4.4+Kernel 3.8+24 bit display

I refer to Andrew Henderson’s wesite http://bbbandroid.sourceforge.net/customize.html to build Android 4.4 on the BBB with 5’’ display. It works fine with 16 bit, but my display is 24 bit, so I refer to this website to change the color from 16bit to 24bit. http://elinux.org/24bit_LCD_for_BBB. “cat /sys/kernel/debug/pinctrl/44e10800.pinmux/pins” shows the setting is correct in the kernel.
pin 8 (44e10820) 00000009 pinctrl-single
pin 9 (44e10824) 00000009 pinctrl-single
pin 10 (44e10828) 00000009 pinctrl-single
pin 11 (44e1082c) 00000009 pinctrl-single
pin 12 (44e10830) 00000009 pinctrl-single
pin 13 (44e10834) 00000009 pinctrl-single
pin 14 (44e10838) 00000009 pinctrl-single
pin 15 (44e1083c) 00000009 pinctrl-single

However, when I check by “logcat | grep gralloc”, it shows 16 bit in Android. Does anyone have any idea or suggestion?

I/gralloc ( 92): bpp = 16
I/gralloc ( 92): r = 11:5
I/gralloc ( 92): g = 5:6
I/gralloc ( 92): b = 0:5