By default zedboard_pulpino will be built without accounting for
pulpino-specific ISA. To account for them, edit
zedboard_pulpino_defconfig and set CONFIG_RISCV_GENERIC_TOOLCHAIN=n.

However, in this case, a pulpino-specific toolchain should be
use, by setting the following env variables, prior to compiling
an application.

export RISCV32_TOOLCHAIN_PATH=~/path/to/pulpino/toolchain
export ZEPHYR_GCC_VARIANT=riscv32