config: add initial openeuler_defconfig for riscv64

riscv inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I8S94P


CVE: NA

---------------------------------

Based on openEuler-23.09 openeuler_defconfig for riscv, use the following
commands introduced in commit ("kconfig: Add script to check & update
openeuler_defconfig") to generate the initial openeuler_defconfig for
OLK-6.6:

cp 23.09_riscv_openeuler_defconfig .config
make save_oedefconfig
make update_oedefconfig

Build and boot testing passed.

Note:
The 23.09_riscv_openeuler_defconfig file is a copy of openEuler-23.09
openeuler_defconfig for riscv.

Signed-off-by: Mingzheng Xing <xingmingzheng@iscas.ac.cn>