[build] Canonicalise image type configuration

Move all image type selection from config/defaults/<platform>.h to the
top-level config/general.h, using indented conditional blocks to
clarify which image types are supported and enabled on each platform.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/config/defaults/efi.h

@@ -36,10 +36,6 @@ FILE_SECBOOT ( PERMITTED );
 
 #define DOWNLOAD_PROTO_FILE	/* Local filesystem access */
 
-#define	IMAGE_EFI		/* EFI image support */
-#define	IMAGE_SCRIPT		/* iPXE script image support */
-#define IMAGE_EFISIG		/* EFI signature list support */
-
 #define	SANBOOT_PROTO_ISCSI	/* iSCSI protocol */
 #define	SANBOOT_PROTO_AOE	/* AoE protocol */
 #define	SANBOOT_PROTO_IB_SRP	/* Infiniband SCSI RDMA protocol */
@@ -71,7 +67,6 @@ FILE_SECBOOT ( PERMITTED );
 #endif
 
 #if defined ( __aarch64__ )
-#define	IMAGE_GZIP		/* GZIP image support */
 #define FDT_CMD
 #endif
 

src/config/defaults/linux.h

@@ -28,8 +28,6 @@ FILE_LICENCE ( GPL2_OR_LATER );
 
 #define DRIVERS_LINUX
 
-#define IMAGE_SCRIPT
-
 #define SANBOOT_PROTO_ISCSI
 #define SANBOOT_PROTO_AOE
 #define SANBOOT_PROTO_IB_SRP

src/config/defaults/pcbios.h

@@ -34,12 +34,6 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 #define IOMAP_VIRT
 #endif
 
-#define	IMAGE_ELF		/* ELF image support */
-#define	IMAGE_MULTIBOOT		/* MultiBoot image support */
-#define	IMAGE_PXE		/* PXE image support */
-#define IMAGE_SCRIPT		/* iPXE script image support */
-#define IMAGE_BZIMAGE		/* Linux bzImage image support */
-
 #define PXE_STACK		/* PXE stack in iPXE - required for PXELINUX */
 #define PXE_MENU		/* PXE menu booting */
 

src/config/defaults/sbi.h

@@ -37,10 +37,6 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 #define SMBIOS_NULL
 #define TIME_NULL
 
-#define IMAGE_SCRIPT
-#define IMAGE_LKRN
-#define IMAGE_GZIP
-
 #define REBOOT_CMD
 #define POWEROFF_CMD
 #define FDT_CMD