Drop explicit NULL initializations from device_operations

Unmentioned fields are initialized with 0 (or NULL) implicitly. Beside
that, the struct has grown over the years. There are too many optional
fields to list them all.

Change-Id: Icb9e14c58153d7c14817bcde148e86e977666e4b
Signed-off-by: Elyes HAOUAS <ehaouas@noos.fr>
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/40126
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/mainboard/emulation/qemu-i440fx/mainboard.c

@@ -36,7 +36,6 @@ static struct device_operations nb_operations = {
 	.set_resources    = pci_dev_set_resources,
 	.enable_resources = pci_dev_enable_resources,
 	.init             = qemu_nb_init,
-	.ops_pci          = 0,
 };
 
 static const struct pci_driver nb_driver __pci_driver = {

src/mainboard/emulation/qemu-i440fx/northbridge.c

@@ -236,8 +236,6 @@ static const char *qemu_acpi_name(const struct device *dev)
 static struct device_operations pci_domain_ops = {
 	.read_resources		= cpu_pci_domain_read_resources,
 	.set_resources		= cpu_pci_domain_set_resources,
-	.enable_resources	= NULL,
-	.init			= NULL,
 	.scan_bus		= pci_domain_scan_bus,
 #if CONFIG(GENERATE_SMBIOS_TABLES)
 	.get_smbios_data	= qemu_get_smbios_data,

src/mainboard/emulation/qemu-q35/mainboard.c

@@ -55,7 +55,6 @@ static struct device_operations nb_operations = {
 	.set_resources    = pci_dev_set_resources,
 	.enable_resources = pci_dev_enable_resources,
 	.init             = qemu_nb_init,
-	.ops_pci          = 0,
 };
 
 static const struct pci_driver nb_driver __pci_driver = {