examples: fix building on arm32

examples: fix building on arm32

Refer to the commit a3c101a61348 ("examples: fix building on arm64")
fix for arm32. crt0.S does not even build with:
    operating system and architecture:
        5.15.0-130-generic x86_64
    installed version of gcc and binutils:
        gcc version 9.4.0 (Ubuntu 9.4.0-1ubuntu1~20.04.3)
    GNU ld (GNU Binutils for Ubuntu) 2.34
    used defconfig:
        stm32h750-art-pi_defconfig
    used commands for building:
        export CROSS_COMPILE=arm-none-eabi- ARCH=arm
        make stm32h750-art-pi_defconfig
        make menuconfig # to add
        make
    examples/api/crt0.S: Assembler messages:
    examples/api/crt0.S:32: Error: lo register required -- `ldr ip,=search_hint'
    examples/api/crt0.S:33: Error: lo register required -- `str sp,[ip]'
    examples/api/crt0.S:39: Error: lo register required -- `ldr ip,=syscall_ptr'
    examples/api/crt0.S:40: Error: lo register required -- `ldr pc,[ip]'
    make[2]: *** [scripts/Makefile.build:292：examples/api/crt0.o] Error 1

Use valid register names and instructions.

Signed-off-by: Liya Huang <1425075683@qq.com>