upgrade kernel uapi to 5.12

[unicornx]

• commit ffb2f6d:

  • use the same 5.12 kernel header file for android-12.0.0_r2, detailed steps refer to description in [Discussion] kernel uapi.h for 12 #9
  • fixed the symbol link bug [bug] libc/versioner-dependencies/riscv64/kernel_uapi_asm-riscv64 is not a sym-link #11

• commit c261119

• due to 5.12 riscv header file doesn't define __ARCH_WANT_RENAMEAT, which means for riscv64, kernel doesn't support syscall for renameat, my solution is define a bionic api by myself and encapsulate calling of renameat2 instead.

I have tested it and build sdk_phone64_riscv64 and run successfully.
I also used the 5.12 header files before and run bionic unit test on 5.10 kenrel before and syscall related cases are passed. Details please refer to https://github.com/aosp-riscv/test-riscv/tree/riscv64-android-12.0.0_dev/bionic/reports.

Note: keep two commits just for better code review experience. Please rebase and squash them before merge.