MIPS: Loongson32: Remove DMA & NAND devices from ls1b/board.c

Commit 7b3415f5

 ("MIPS: Loongson32: Remove unused platform devices")
removed the definitions of platform devices which have no in tree
drivers from common Loongson32 code, but missed their removal from
Loongson 1B board code in arch/mips/loongson32/ls1b/board.c. This causes
build failures due to the missing declarations of ls1x_dma_pdev,
ls1x_nand_pdev & their associated *_set_platdata functions.

Remove the dead code from arch/mips/loongson32/ls1b/board.c to fix the
build.

Signed-off-by: Paul Burton <paul.burton@mips.com>
Fixes: 7b3415f5 ("MIPS: Loongson32: Remove unused platform devices")