part: efi: Add a Kconfig option for the number of partition entries

On some SoCs, the SPL needs to be located right in the middle of the GPT
partition entries.

One way to work around that is to create partition entries for a smaller
number of partitions to accomodate with where the SPL will be. Create a
Kconfig option to allow to do that.

Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>

disk/Kconfig

@@ -78,6 +78,19 @@ config EFI_PARTITION
 	  common when EFI is the bootloader.  Note 2TB partition limit;
 	  see disk/part_efi.c
 
+config EFI_PARTITION_ENTRIES_NUMBERS
+	int "Number of the EFI partition entries"
+	depends on EFI_PARTITION
+	default 128
+	help
+	  Specify the number of partition entries in the GPT. This is
+	  meant to allow less than the standard specifies for devices
+	  that might need to place their first-stage bootloader in the
+	  middle of a regular GPT.
+
+	  If unsure, leave at 128 entries, which is the standard
+	  number.
+
 config EFI_PARTITION_ENTRIES_OFF
         int "Offset (in bytes) of the EFI partition entries"
 	depends on EFI_PARTITION

include/part_efi.h

@@ -27,7 +27,7 @@
 #define GPT_HEADER_SIGNATURE 0x5452415020494645ULL
 #define GPT_HEADER_REVISION_V1 0x00010000
 #define GPT_PRIMARY_PARTITION_TABLE_LBA 1ULL
-#define GPT_ENTRY_NUMBERS		128
+#define GPT_ENTRY_NUMBERS		CONFIG_EFI_PARTITION_ENTRIES_NUMBERS
 #define GPT_ENTRY_SIZE			128
 
 #define PARTITION_SYSTEM_GUID \