dt-bindings: interrupt-controller: Add Sophgo sg2042 CLINT mswi

dt-bindings: interrupt-controller: Add Sophgo sg2042 CLINT mswi

The clint of Sophgo's sg2042 is based off IP designed by T-HEAD, and
implements the not yet frozen ACLINT spec. This spec seems to be
abandoned, and will not be frozen in the predictable future.
Frozen specs required by the RISC-V maintainers before merging content
relating to those extensions, therefore a generic compatible is not
appropriate.
Instead, add new vendor specific compatible strings to identify mswi of
sg2042 clint.

Signed-off-by: Inochi Amaoto <inochiama@outlook.com>
Signed-off-by: Chen Wang <unicorn_wang@outlook.com>
[conor: re-wrote commit message to drop irrelevant sifive,clint discussion]
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>