migrate NXP Kinetis khci to chipidea ci_fs driver (device + host)

Complete the khci -> chipidea ci_fs migration that was started for device
(commit d70403f1f "host is not yet"):

- device: switch kinetis_k/kl/k32l (Makefiles + k32l CMake) to dcd_ci_fs.c
- host: add hcd_ci_fs.c (port of hcd_khci.c onto ci_fs_regs_t) and switch all
  Kinetis families to it; remove src/portable/nxp/khci entirely
- enable host examples (device_info, cdc_msc_hid) for mcu:KINETIS_K
- README: merge the KL and K32L2 rows into a single "KL, K32L" ci_fs row

hcd_ci_fs.c also fixes two pre-existing host bugs found via HIL on frdm_k64f
(present in the old hcd_khci.c too):
- data toggle was flipped on a NAK in suspend_transfer; a NAK transfers no
  data so the toggle must be preserved, else the retried bulk packet is
  silently discarded by the device (MSC CBW/CSW hang). See comment in file.
- prepare_packets asserted and dropped a transfer when the single shared BDT
  was still owned by an in-flight transfer under concurrent activity; now it
  returns busy and resume_transfer defers/retries on the next SOF.

HIL verified on frdm_k64f: device 13/13, host cdc_msc_hid (CDC mount + echo +
MSC mount, through a hub).

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>
Claude-Session: https://claude.ai/code/session_01ExGPLP5eU43LR7o6yYLpNi

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