memblock tests: fix undefined reference to `panic'

memblock tests: fix undefined reference to `panic'

commit e96c6b8f212a ("memblock: report failures when memblock_can_resize
is not set") introduced the usage of panic, which is not defined in
memblock test.

Let's define it directly in panic.h to fix it.

Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
CC: Song Shuai <songshuaishuai@tinylab.org>
CC: Mike Rapoport <rppt@kernel.org>
Link: https://lore.kernel.org/r/20240402132701.29744-3-richard.weiyang@gmail.com
Signed-off-by: Mike Rapoport (IBM) <rppt@kernel.org>