feat(driver): BitScrambler support

This adds an assembler for the BitScrambler assembly language,
plus unit tests for it. It also adds the loopback driver,
which can do BitScrambler operations on memory-to-memory
transfers. Documentation is also included.

tools/test_bsasm/testcases/sanity.bsasm

@@ -0,0 +1,13 @@
+#Example bitscrambler program. Does nothing but forward all bytes.
+
+cfg trailing_bytes 0			#End program as soon as the input EOFs.
+cfg prefetch true				#We expect M0/M1 to be filled
+cfg lut_width_bits 8			#Not really applicable here
+
+loop:
+	set 0..15 0..15,
+	set 16..23 H,
+	set 24..31 L,
+	write 32,
+	read 32,
+	jmp loop