[smart] Fix bugs on lwp kill

[polarvid]

拉取/合并请求描述：(PR description)

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为什么提交这份PR (why to submit this PR)

Issues 1: lwp kill will not terminate process occasionally.

Previous implementation only allow main thread in a process to do the termination. If the termination is triggered by a sub-thread while main thread is suspended, the process will hang up forever.

Issues 2: sigtimedwait should reset the signal mask whlie suspended.

Issues 3: context switch will corrupt the SPSR

The user status may be corrupted during rt_schedule() because of this.

rt-thread/libcpu/aarch64/common/context_gcc.S

Line 147 in 5c4b44f

MOV X19, #((3 << 6) | 0x4 | 0x1) /* el1h, disable interrupt */

你的解决方案是什么 (what is your solution)

For issue 1:

In lwp_termiante(), each thread can race to terminate the process, which will set a flag to other threads to indicate a termination is pending and request all the threads to exit. Still, after every other threads exit, the main thread only will complete the remaining termination progress (setup return code, etc.)

For issue 3:

This patch bypass this through constructing the SPSR context explictly in stack frame of user exception. And restore it after re-schedule.

在什么测试环境下测试通过 (what is the test environment)

A1000, QEMU aarch64

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当前拉取/合并请求的状态 Intent for your PR

必须选择一项 Choose one (Mandatory):

• 本拉取/合并请求是一个草稿版本 This PR is for a code-review and is intended to get feedback
• 本拉取/合并请求是一个成熟版本 This PR is mature, and ready to be integrated into the repo

代码质量 Code Quality：

我在这个拉取/合并请求中已经考虑了 As part of this pull request, I've considered the following:

• 已经仔细查看过代码改动的对比 Already check the difference between PR and old code
• 代码风格正确，包括缩进空格，命名及其他风格 Style guide is adhered to, including spacing, naming and other styles
• 没有垃圾代码，代码尽量精简，不包含#if 0代码，不包含已经被注释了的代码 All redundant code is removed and cleaned up
• 所有变更均有原因及合理的，并且不会影响到其他软件组件代码或BSP All modifications are justified and not affect other components or BSP
• 对难懂代码均提供对应的注释 I've commented appropriately where code is tricky
• 代码是高质量的 Code in this PR is of high quality
• 已经使用formatting 等源码格式化工具确保格式符合RT-Thread代码规范 This PR complies with RT-Thread code specification