lib: utils/ipi: mswi: add T-Head C9xx CLINT compatible

Althoug the MTIMER part of a C9xx CLINT differs from a SiFive one, the
MSWI part is compliant.

Add T-Head C9xx CLINT compatible string to fdt_ipi_mswi code, sharing
the same codepath with SiFive CLINT.

Signed-off-by: Icenowy Zheng <uwu@icenowy.me>
Reviewed-by: Anup Patel <anup@brainfault.org>