Some U-Boot configurations use lzop, which may not be available on the
build machine since it's not a mandatory dependency of Buildroot.
To solve this, a new option BR2_TARGET_UBOOT_NEEDS_LZOP is introduced,
and handled in a similar way to the existing
BR2_TARGET_UBOOT_NEEDS_OPENSSL option.
This fixes the build of the dra7xx_evm U-Boot defconfig as of U-Boot
2018.07, on a build machine without lzop installed.
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
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