Datasheet

OK since you're not going to run the helper, lets add the device tree overlay manually. Edit /boot/config.txt with

sudo nano /boot/config.txt

and add the following lines at the end:

[pi1]

device_tree=bcm2708-rpi-b-plus.dtb

[pi2]

device_tree=bcm2709-rpi-2-b.dtb

[all]

dtparam=spi=on

dtparam=i2c1=on

dtparam=i2c_arm=on

dtoverlay=pitft28r,rotate=90,speed=32000000,fps=20