sys/crypto: aarch64: Catch up with builtin rename for GCC12

Kernel self tests successfully pass for aarch64{,eb}.

Same binary generated by GCC10 and GCC12 for:
---
#include <sys/types.h>
#include "arm_neon.h"

uint32x4_t my_vshrq_n_u32(uint32x4_t v, uint8_t bits)
{
return vshrq_n_u32(v, bits);
}

uint8x16_t my_vshrq_n_u8(uint8x16_t v, uint8_t bits)
{
return vshrq_n_u8(v, bits);
}
---

sys/crypto: Introduce arch/{arm,x86} to share common MD headers

Dedup between aes and chacha. No binary changes.

sys/crypto: Introduce arch/{arm,x86} to share common MD headers

Dedup between aes and chacha. No binary changes.