FLAT-family opcode 0x25 (FLAT/GLOBAL/SCRATCH_LOAD_SHORT_D16_HI) loads an
unsigned halfword into bits [31:16] of the destination and keeps bits [15:0].
Decode it beside the low-half variant and let it select the high half of the
existing partial destination write, so FLAT_LOAD needs no new path.
Ghost of Yotei CS 0x79b0066f0cd1f3cd stopped at
global_load_short_d16_hi v16, v18, s[0:1] offset:196 (0xdc9480c4 0x10000012).
