drivers: charger: charger_max20355: fix configuration

Maximum charging current is selected with an external resistor in
the MAX20335 charger. Therefore it is not possible to configure it
with software directly. There is only a capability to limit current
set with hardware but configuration of the limiter is not
straight-forward.

To reflect real functionality, drop usage of
`constant-charge-current-max-microamp` property as an required one and
use custom `chgin-to-sys-current-limit-microamp` instead.
Use enum in binding file to signalize improper values at compile time.

Drop support for `CHARGER_PROP_CONSTANT_CHARGE_CURRENT_UA` API property
since this cannot be handled.

The `max20335_get_constant_charge_current()` function become useless so
remove it.

Signed-off-by: Lukasz Madej <l.madej@grinn-global.com>

dts/bindings/charger/maxim,max20335-charger.yaml

@@ -8,12 +8,21 @@ include: battery.yaml
 compatible: "maxim,max20335-charger"
 
 properties:
-  constant-charge-current-max-microamp:
-    required: true
-
   constant-charge-voltage-max-microvolt:
     required: true
 
+  chgin-to-sys-current-limit-microamp:
+    type: int
+    required: true
+    enum:
+      - 0
+      - 100000
+      - 500000
+      - 1000000
+    description: |
+      CHGIN to SYS path current limitter configuration.
+      Refer to ILimCntl register description for details.
+
   int-gpios:
     type: phandle-array
     required: true