[Dark Cloud 2] Runtime lacks 4HH/4HL transfer and sampling support

[tealalchemist]

The functions processImage and samplePoint need support for 4HH/4HL.
4HH and 4HL unpack into the hi and low nybbles of a 32 bit vram word
Sampling is similar to P4 but taking into account the location of the nybbles from the transfer