u-boot: set UBOOT_MACHINE

Set UBOOT_MACHINE to hikirk_config to avoid errors compiling u-boot-fw-utils.
Add hikirk_board_support.patch to u-boot-fw-utils recipe. Because the hikirk
u-boot configuration is needed.

Signed-off-by: Mario Schuknecht <schuknecht@dresearch-fe.de>