kernel/rv1106: HPMCU mailbox 100% VERIFIED + open NPU driver VERIFIED

MAILBOX (fully open A7<->RISC-V SCR1 round-trip, 5/5 exact echoes on c8a3):
- rockchip-mailbox.c: rv1106 has 1 shared IRQ, not 4/channel -> added
  rv1106_drv_data{num_chans=1} + compatible (rk3368 fallback assumed 4 -> probe
  failed 'IRQ index 1 not found').
- clk-rv1106.c: CLK_CORE_MCU (SCR1 core clock) marked CLK_IGNORE_UNUSED -
  6.18's clk_disable_unused() was switching off the coprocessor clock so a
  loaded firmware never ran (5.10 left it on).
- Open SCR1 echo firmware (scr1-echo/, 154B RV32IMC) + load/test scripts;
  A2B_INTEN on the MCU side + CMD-then-DAT (DAT=doorbell) order. Loaded via the
  proven hpmcu.rs SRAM path; do NOT kill warden-flared (dw-wdt). mailbox/VERIFIED.md.

NPU (open GPL rknpu 0.9.2 kernel driver on 6.18):
- DT fix: base npu node lacks interrupt-names, driver requests IRQ byname
  'npu_irq' -> probe bailed -ENXIO. Added interrupt-names='npu_irq'.
- Verified: [drm] Initialized rknpu 0.9.2 on minor 1; /dev/dri/card1;
  rknpu_version_test PASS (0.9.2 + hw version, full power/clock/reset path).
- Honest ceiling: open compute (regcmd compiler) is a from-scratch ~person-year
  RE project, no RV1106 prior art; ship the driver, no blob. npu/VERIFIED.md.

DRIVER-PARITY + CAPABILITIES-AUDIT updated; dts snapshot refreshed.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017wB8KB3MMQztRDXCMCkPrf

kernel/rv1106-enablement/mailbox/scr1-echo/Makefile

@@ -0,0 +1,37 @@
+# HPMCU mailbox-echo firmware — bare-metal RV32IMC for the RV1106 SCR1 core.
+# Same xPack riscv-none-embed-gcc 10.2.0 + flags as the watchdog firmware.
+
+XPACK ?= <flare-edge>/sdk/sysdrv/source/mcu/prebuilts/gcc/linux-x86/riscv64/xpack-riscv-none-embed-gcc-10.2.0-1.2/bin
+CROSS ?= $(XPACK)/riscv-none-embed-
+
+CC      = $(CROSS)gcc
+OBJCOPY = $(CROSS)objcopy
+SIZE    = $(CROSS)size
+
+CFLAGS  = -march=rv32imc -mabi=ilp32 -mcmodel=medany -Os -g \
+          -ffreestanding -nostdlib -fno-builtin \
+          -ffunction-sections -fdata-sections -Wall -Wextra
+LDFLAGS = -T link.lds -nostdlib -Wl,--gc-sections -Wl,-Map=mailbox-echo.map
+
+OBJS = start.o main.o
+
+all: hpmcu-mailbox-echo.bin
+
+hpmcu-mailbox-echo.elf: $(OBJS) link.lds
+	$(CC) $(CFLAGS) $(LDFLAGS) -o $@ $(OBJS)
+	$(SIZE) $@
+
+hpmcu-mailbox-echo.bin: hpmcu-mailbox-echo.elf
+	$(OBJCOPY) -O binary $< $@
+	@ls -la $@
+
+%.o: %.c
+	$(CC) $(CFLAGS) -c -o $@ $<
+
+%.o: %.S
+	$(CC) $(CFLAGS) -c -o $@ $<
+
+clean:
+	rm -f *.o *.elf *.bin *.map
+
+.PHONY: all clean