Add initial support for the Milk-V Duo board.

The Sophgo CV1800B SoC features T-Head C906 processing, standard PLIC
and CLINT controllers, a dw8250 uart, and basic clock control. Combined
with simple stubs for custom T-Head PMU CSRs, the current
implementation can successfully run OpenSBI and boot Linux v7.0 from an
SD card to the Linux shell.
---
Changes in v2:
- Added link for the custom T-Head PMU CSRs
- Added qtest to validate basic for the dw8250 and clock controller.
- Removed RFC tag.

Kuan-Wei Chiu (6):
  target/riscv: Add stubs for T-Head PMU CSRs
  hw/char: Add dw8250 UART
  hw/misc: Add Sophgo CV1800B clock controller
  hw/riscv: Add Sophgo CV1800B SoC support
  hw/riscv: Add Milk-V Duo board support
  tests/qtest: Add qtest for Milk-V Duo board

 MAINTAINERS                                 |  12 ++
 configs/devices/riscv64-softmmu/default.mak |   1 +
 hw/char/Kconfig                             |   4 +
 hw/char/dw8250.c                            | 118 ++++++++++++++
 hw/char/meson.build                         |   1 +
 hw/misc/Kconfig                             |   3 +
 hw/misc/cv1800b_clk.c                       |  89 +++++++++++
 hw/misc/meson.build                         |   1 +
 hw/riscv/Kconfig                            |  14 ++
 hw/riscv/cv1800b.c                          | 168 ++++++++++++++++++++
 hw/riscv/meson.build                        |   3 +
 hw/riscv/milkv_duo.c                        | 122 ++++++++++++++
 include/hw/char/dw8250.h                    |  27 ++++
 include/hw/misc/cv1800b_clk.h               |  24 +++
 include/hw/riscv/cv1800b.h                  |  52 ++++++
 target/riscv/th_csr.c                       |  30 ++++
 tests/qtest/meson.build                     |   3 +-
 tests/qtest/milkv-duo-test.c                |  70 ++++++++
 18 files changed, 741 insertions(+), 1 deletion(-)
 create mode 100644 hw/char/dw8250.c
 create mode 100644 hw/misc/cv1800b_clk.c
 create mode 100644 hw/riscv/cv1800b.c
 create mode 100644 hw/riscv/milkv_duo.c
 create mode 100644 include/hw/char/dw8250.h
 create mode 100644 include/hw/misc/cv1800b_clk.h
 create mode 100644 include/hw/riscv/cv1800b.h
 create mode 100644 tests/qtest/milkv-duo-test.c

-- 
2.54.0.563.g4f69b47b94-goog