Generic MTK RGU mapped register reset driver

This is a reset driver using toprgu to map its non-volatile register.
The reset is generally performed with a write to the non-volatile register
defined by the register map pointed by toprgu reference plus the offset
with the mask defined in the reboot-mode node.

Required properties:
- compatible: should contain "toprgu-reboot-mode"
- regmap: this is phandle to the register map node
- offset: offset in the register map for the reboot-mode register (in bytes)
- mask: the reset value written to the reboot register (32 bit access)

Examples:
	reboot-mode {
	   compatible = "toprgu-reboot-mode";
	   regmap = <&toprgu>;
	   offset = <0x24>;
	   mask = <0xF>;
	};

Optional properties - reboot mode value that will keep in toprgu nonrst RG:
- mode-charger = <BOOT_CHARGER>;
- mode-recovery = <BOOT_RECOVERY>;
- mode-bootloader = <BOOT_BOOTLOADER>;
- mode-dm-verity-dev-corrupt = <BOOT_DM_VERITY>;
- mode-kpoc = <BOOT_KPOC>;
- mode-ddr-reserve = <BOOT_DDR_RSVD>;
- mode-meta = <BOOT_META>;
- mode-rpmbpk = <BOOT_RPMBPK>;