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

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>