bscan: rename from bscan_spi, add TAP primitives for the SVF player

The module outgrew its "SPI bridge" name — it's mostly generic
single-device JTAG TAP primitives now. Rename modules/bscan_spi ->
modules/bscan (dir, files, library target, includes, doc paths);
bscan_* function names and bscan_spi_xfer() kept.

Add the two primitives the SVF player needs beyond shift_dr:
- bscan_shift_ir: general IR scan with TDO capture (bscan_set_ir is
  opcode-only, no readback)
- bscan_tap_reset: force Test-Logic-Reset, land in Run-Test/Idle

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

doc/tutorial.md

@@ -357,7 +357,7 @@ read-latency skew.
 ### The transfer primitive
 
 `bscan_spi_xfer(jc, t, tx, txlen, rx, rxlen)` in
-`modules/bscan_spi/bscan_spi.c` performs one CS-framed transaction:
+`modules/bscan/bscan.c` performs one CS-framed transaction:
 clock out `txlen` MOSI bytes, then read `rxlen` MISO bytes. It builds
 the quartiq/OpenOCD jtagspi DR frame
 (`marker | bit-count | MOSI | latency-skip | MISO`) and matches