dt-bindings: timer: thead,c900-aclint-mtimer: separate mtime and mtimecmp regs

The timer registers of aclint don't follow the clint layout and can
be mapped on any different offset. As sg2042 uses separated timer
and mswi for its clint, it should follow the aclint spec and have
separated registers.

The previous patch introduced a new type of T-HEAD aclint timer which
has clint timer layout. Although it has the clint timer layout, it
should follow the aclint spec and uses the separated mtime and mtimecmp
regs. So a ABI change is needed to make the timer fit the aclint spec.

To make T-HEAD aclint timer more closer to the aclint spec, use
regs-names to represent the mtimecmp register, which can avoid hack
for unsupport mtime register of T-HEAD aclint timer.

Also, as T-HEAD aclint only supports mtimecmp, it is unnecessary to
implement the whole aclint spec. To make this binding T-HEAD specific,
only add reg-name for existed register. For details, see the discussion
in the last link.

Signed-off-by: Inochi Amaoto <inochiama@outlook.com>
Fixes: 4734449f73 ("dt-bindings: timer: Add Sophgo sg2042 CLINT timer")
Link: https://lists.infradead.org/pipermail/opensbi/2023-October/005693.html
Link: https://github.com/riscv/riscv-aclint/blob/main/riscv-aclint.adoc
Link: https://lore.kernel.org/all/IA1PR20MB4953F9D77FFC76A9D236922DBBB6A@IA1PR20MB4953.namprd20.prod.outlook.com/
Acked-by: Guo Ren <guoren@kernel.org>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/IA1PR20MB49531ED1BCC00D6B265C2D10BB86A@IA1PR20MB4953.namprd20.prod.outlook.com

Documentation/devicetree/bindings/timer/thead,c900-aclint-mtimer.yaml

@@ -17,7 +17,12 @@ properties:
       - const: thead,c900-aclint-mtimer
 
   reg:
-    maxItems: 1
+    items:
+      - description: MTIMECMP Registers
+
+  reg-names:
+    items:
+      - const: mtimecmp
 
   interrupts-extended:
     minItems: 1
@@ -28,6 +33,7 @@ additionalProperties: false
 required:
   - compatible
   - reg
+  - reg-names
   - interrupts-extended
 
 examples:
@@ -39,5 +45,6 @@ examples:
                             <&cpu3intc 7>,
                             <&cpu4intc 7>;
       reg = <0xac000000 0x00010000>;
+      reg-names = "mtimecmp";
     };
 ...