sysreset: Add -c flag for explicit cold reset

Add support for reset -c flag to explicitly request cold reset.
This provides symmetry with -w (warm) and -u (firmware UI) flags.

For EFI apps, this performs EFI_RESET_COLD which does a full system
reboot without going to firmware setup interface.

Series-to: concept
Series-cc: heinrich
Cover-letter:
efi: Improve integration of the app with a Shim environment
This series collects together various small fixes and improvements which
make it easier to use the U-Boot EFI app in a bootflow which includes
Shim:

- 'Reset' back to the caller (e.g. EDK2)
- Machine reset using cold and warm reset
- Reset and enter the firmware UI
- Shim command now supports persistent debug
- Bootmenu shows the real media for each bootflow rather than just 'efi'
END

Signed-off-by: Simon Glass <sjg@chromium.org>

lib/efi_client/efi_app.c

@@ -254,6 +254,10 @@ static int efi_sysreset_request(struct udevice *dev, enum sysreset_t type)
 	struct efi_priv *priv = efi_get_priv();
 
 	switch (type) {
+	case SYSRESET_COLD:
+		/* Perform a cold reset */
+		priv->run->reset_system(EFI_RESET_COLD, EFI_SUCCESS, 0, NULL);
+		break;
 	case SYSRESET_TO_FIRMWARE_UI: {
 		efi_status_t ret;
 		u64 osind;