configs/imx7dpico: Bump Linux and U-Boot

configs/imx7dpico: Bump Linux and U-Boot

Bump Linux to 5.1 and U-Boot to version 2019.01.

U-Boot patch is no longer needed, applied upstream.

U-Boot defconfig name for this board has changed to pico-pi-imx7d.

U-Boot now supports distrobootcmd for this board, so add the appropriate
extlinux.conf and use SPL+u-boot.img instead of u-boot.imx. Note that
the common freescale post-image script handles things appropriately
based on the selected options in .config.

dosfstools and mtools are no longer needed to build the image.

Signed-off-by: Joris Offouga <offougajoris@gmail.com>
Tested-by: Pierre-Jean Texier <pjtexier@koncepto.io>
[Arnout: remove BR2_PACKAGE_HOST_DOSFSTOOLS and BR2_PACKAGE_HOST_MTOOLS]
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>