riscv: u-boot-spl.lds: Remove _image_binary_end alignment

riscv: u-boot-spl.lds: Remove _image_binary_end alignment

The _image_binary_end symbol was aligned to the 8-bytes boundary.
However, the SPL device tree (u-boot-spl.dtb) is concatenated right
after the binary (u-boot-spl-nodtb.bin) wihtout the consideration of
the 8-bytes alignment restriction.

After then, for the SPL_SEPARATE_BSS case, fdtdec_setup() searching
for the DTB by _image_binary_end will return the "Missing DTB" error.
As the real DTB starting point does not align to a 8-bytes address
like _image_binary_end does.

Signed-off-by: Chia-Wei Wang <chiawei_wang@aspeedtech.com>
Reviewed-by: Leo Yu-Chi Liang <ycliang@andestech.com>