riscv: defconfig: add lanxin soc basic support

[gougou1104]

Add basic support for lanxin's lx500 soc, just add PL011 seral port for debug purpose and enable RISCV ISA V to fix illegal instruction exception caused by systemd.

[github-actions]

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开始测试 log: https://github.com/RVCK-Project/rvck/actions/runs/26636156603

参数解析结果

args	value
repository	RVCK-Project/rvck
head ref	pull/294/head
base ref	rvck-6.6
LAVA repo	RVCK-Project/lavaci
LAVA hardware	['qemu']
LAVA Testcase path	lava-testcases/common-test/ltp/ltp.yaml
need run job	kunit-test,kernel-build,check-patch,lava-trigger

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测试完成

详细结果:

check	result
kunit-test	success
kernel-build	failure
check-patch	success
lava-trigger-qemu	skipped
lava-trigger-sg2042	skipped
lava-trigger-k1	skipped
lava-trigger-lpi4a	skipped

Kunit Test Result

[12:07:47] Testing complete. Ran 457 tests: passed: 445, skipped: 12

• detail log: https://github.com/RVCK-Project/rvck/actions/runs/26636156603/attempts/1/#summary-78496883082

Kernel Build Result

• Kernel build failed.

• detail log: https://github.com/RVCK-Project/rvck/actions/runs/26636156603/attempts/1/#summary-78496882949

Check Patch Result

Total Errors	0
Total Warnings	1

• detail log: https://github.com/RVCK-Project/rvck/actions/runs/26636156603/attempts/1/#summary-78496883002