loader: use display pixel density for font autoselection

Calculate font size from 16 density independent pixels (dp) by using:
size = 16 * ppi/160 * display_factor

We are specifying font size 16dp, and assuming 1dp = 160ppi.
Also apply scaling factor 2 (display_factor).

(cherry picked from commit becaac3972f1fde4e3c44516399468ba5ca65c9b)

Approved by: re (gjb)