arm64_task/pthread_start: Convert the C / inline ASM code to assembly

[pussuw]

Summary

The aforementioned functions can/will fail if the C compiler decides to use the stack for the incoming entrypt/etc. parameters.

Fix this issue by converting the jump to user part into pure assembly, ensuring the stack is NOT used for the parameters.

Impact

Fix system crash when user process enters userspace

Testing

QEMU + IMX9 with kernel mode

[pussuw]

Second attempt at this. The original fix can break due to the C compiler pushing the incoming arguments to stack (for no reason, but it CAN do it so it will happen). Fix the issue by removing the C compiler from the equation by implementing the whole thing in assembly.

[pussuw]

@acassis (or someone) could you please help me here by re-starting the CI tests:

/usr/bin/bash: line 1: arm-nuttx-eabi-gcc: command not found
Disabling CONFIG_ARM_TOOLCHAIN_BUILDROOT
Enabling CONFIG_ARM_TOOLCHAIN_GNU_EABI
Building NuttX...
make[1]: *** No rule to make target '/github/workspace/sources/nuttx/.config'.
make[1]: Failed to remake makefile '/github/workspace/sources/nuttx/.config'.
make: *** [tools/Unix.mk:273: tools/cnvwindeps] Error 2
make: Target 'all' not remade because of errors.
/github/workspace/sources/nuttx/tools/testbuild.sh: line 385: /github/workspace/sources/nuttx/../nuttx/nuttx.manifest: No such file or directory

I don't think this has anything to do with my patches