Define DES-specific 28-bit _rotLeft().

algorithms/encryption/des/src/des.c
	-Define `_rotLeft()`, because DES requires that its left
	rotation operates on the first 28-bits of a byte array, so
	`BitOps_rotLeft()` wouldn't work (as it operates on entire bytes
	at a time, and would thus have to select between 24 and 32).