target: Drop se_subsystem_api->[write_cache,fua_write]_emulated flags

This patch drops se_subsystem_api->[write_cache,fua_write]_emulated flags
set by viritual FILEIO/IBLOCK/RD_MCP backend drivers in favor of explict
TRANSPORT_PLUGIN_PHBA_PDEV checks to know when to fail if userspace is
attempting to set virtual emulation bits for an pSCSI (passthrough)
backend device.

Reported-by: Christoph Hellwig <[e-mail]>
Cc: Christoph Hellwig <[e-mail]>
Signed-off-by: Nicholas Bellinger <[e-mail]>

drivers/target/target_core_device.c

···
 		return -EINVAL;
 	}
 
-	if (flag && dev->transport->fua_write_emulated == 0) {
-		pr_err("fua_write_emulated not supported\n");
+	if (flag &&
+	    dev->transport->transport_type == TRANSPORT_PLUGIN_PHBA_PDEV) {
+		pr_err("emulate_fua_write not supported for pSCSI\n");
 		return -EINVAL;
 	}
 	dev->se_sub_dev->se_dev_attrib.emulate_fua_write = flag;
···
 		pr_err("Illegal value %d\n", flag);
 		return -EINVAL;
 	}
-	if (flag && dev->transport->write_cache_emulated == 0) {
-		pr_err("write_cache_emulated not supported\n");
+	if (flag &&
+	    dev->transport->transport_type == TRANSPORT_PLUGIN_PHBA_PDEV) {
+		pr_err("emulate_write_cache not supported for pSCSI\n");
 		return -EINVAL;
 	}
 	dev->se_sub_dev->se_dev_attrib.emulate_write_cache = flag;

drivers/target/target_core_file.c

···
 	.name			= "fileio",
 	.owner			= THIS_MODULE,
 	.transport_type		= TRANSPORT_PLUGIN_VHBA_PDEV,
-	.write_cache_emulated	= 1,
-	.fua_write_emulated	= 1,
 	.attach_hba		= fd_attach_hba,
 	.detach_hba		= fd_detach_hba,
 	.allocate_virtdevice	= fd_allocate_virtdevice,

drivers/target/target_core_iblock.c

···
 	.name			= "iblock",
 	.owner			= THIS_MODULE,
 	.transport_type		= TRANSPORT_PLUGIN_VHBA_PDEV,
-	.write_cache_emulated	= 1,
-	.fua_write_emulated	= 1,
 	.attach_hba		= iblock_attach_hba,
 	.detach_hba		= iblock_detach_hba,
 	.allocate_virtdevice	= iblock_allocate_virtdevice,

drivers/target/target_core_rd.c

···
 static struct se_subsystem_api rd_mcp_template = {
 	.name			= "rd_mcp",
 	.transport_type		= TRANSPORT_PLUGIN_VHBA_VDEV,
-	.write_cache_emulated	= 1,
 	.attach_hba		= rd_attach_hba,
 	.detach_hba		= rd_detach_hba,
 	.allocate_virtdevice	= rd_allocate_virtdevice,

include/target/target_core_backend.h

···
 
 	u8 transport_type;
 
-	unsigned int fua_write_emulated : 1;
-	unsigned int write_cache_emulated : 1;
-
 	int (*attach_hba)(struct se_hba *, u32);
 	void (*detach_hba)(struct se_hba *);
 	int (*pmode_enable_hba)(struct se_hba *, unsigned long);