Bring up minos on the Allwinner D1 (Lichee RV) over FEL/xfel and add
bidirectional UART so the console can read keystrokes, not just print.
D1 / Lichee RV boot:
- riscv arch.c: select UART0 base by -DBOARD_D1 (0x02500000 vs QEMU
0x10000000) and add a reg-shift abstraction (uart_rd/uart_wr): the D1's
Synopsys DW-8250 uses 32-bit registers at 4-byte spacing, which is what
made the first hardware boot silent.
- d1_uart0_init(): gate/deassert UART0 clock, mux PB8/PB9 to UART0, set
115200 8N1, clear FIFOs, force non-loopback, drain stale RX.
- link-d1.ld: link for DRAM at 0x40000000 (xfel exec target, M-mode).
- Makefile: 'lichee' builds the flat binary; 'run-lichee' loads it via
xfel (ddr d1 / write / exec).
- arch_name() reports the concrete board.
UART input (all archs):
- arch contract gains arch_uart_getc() and arch_uart_rx_ready(),
implemented for riscv, x86 (COM1) and arm (Cadence UART).
- console gains getc() and drain_rx().
- kmain() runs an interactive echo loop (seed of the M3 console).
Verified: echo works under QEMU on x86/riscv/arm, and on real D1
hardware (banner once, then live keystroke echo over UART0 @115200).
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