clk: add Siflower SF21 topcrm support

Siflower SF21A6826 and SF21H8898 are RISC-V chips with quad-core
T-Head C908 for home routers and gateways.
This series adds the initial RISC-V Kconfig entry for Siflower SoCs and
support for the toplevel clock and reset module on Siflower SF21 socs.

Signed-off-by: Chuanhong Guo <gch981213@gmail.com>
---
Changes in v2:
- drop "if TTY" condition in ARCH_SIFLOWER
- drop "xin25m" in dt bindings for the possibility of a different
  xtal frequency.
- use index instead of fw_name for xtal clock in the driver.
- drop unnecessary fixed-clock node in dt binding example.
- name the top node "soc" instead of "/" to fix binding check
  failure on missing "model" and "compatible".
- drop SF21_RESET_MAX, rename SF21_CLK_MAX to SF21_NUM_CLKS and
  define it in driver instead of binding header.
- split dt binding header into separated clock and reset headers.
- sort headers in the driver
- add a shared sf21_dual_dividers for the two dividers in series
  in CMNPLL and PCIEPLL.
- multiply before divide for PLL VCO calculations.
- change cpu and pic clock flags from ignore_unused to is_critical.
- use guard macro for spinlocks.
- split clock and reset locks and use raw_spinlock for clock lock.
- select RATIONAL in Kconfig for clk driver.
- use FIELD_MAX instead of BIT(x) - 1 for field max value.

- Link to v1: https://lore.kernel.org/r/20260517-sf21-topcrm-v1-0-438f2...

---
Chuanhong Guo (3):
      riscv: add Siflower RISC-V SoC family Kconfig support
      dt-bindings: clock: add header/doc for Siflower sf21-topcrm
      clk: add support for siflower sf21-topcrm

 .../bindings/clock/siflower,sf21-topcrm.yaml       |   60 ++
 arch/riscv/Kconfig.socs                            |    7 +
 drivers/clk/Kconfig                                |    1 +
 drivers/clk/Makefile                               |    1 +
 drivers/clk/siflower/Kconfig                       |   23 +
 drivers/clk/siflower/Makefile                      |    1 +
 drivers/clk/siflower/clk-sf21-topcrm.c             | 1017 ++++++++++++++++++++
 include/dt-bindings/clock/siflower,sf21-topcrm.h   |   42 +
 include/dt-bindings/reset/siflower,sf21-topcrm.h   |   25 +
 9 files changed, 1177 insertions(+)
---
base-commit: c1ecb239fa3456529a32255359fc78b69eb9d847
change-id: 20260515-sf21-topcrm-1856c05b6138

Best regards,
-- 
Chuanhong Guo <gch981213@gmail.com>