[libcpu][risc-v] fix the bug when using ASID in the RV64 MMU

* (fix) mmu: satp value should be 64-bit
Corrected the SATP register to ensure it uses the correct 64-bit format as required by the system architecture.

* use __asm__ instead of asm for the GNU C compiler

Co-authored-by: Shell <smokewood@qq.com>

---------

Co-authored-by: Shell <smokewood@qq.com>

libcpu/risc-v/common64/asid.c

@@ -29,9 +29,10 @@ static rt_uint64_t global_asid_generation;
 
 void rt_hw_asid_init(void)
 {
-    unsigned int satp_reg = read_csr(satp);
+    rt_uint64_t satp_reg = read_csr(satp);
     satp_reg |= (((rt_uint64_t)0xffff) << PPN_BITS);
     write_csr(satp, satp_reg);
+    __asm__ volatile("sfence.vma x0, x0");
     unsigned short valid_asid_bit = ((read_csr(satp) >> PPN_BITS) & 0xffff);
 
     // The maximal value of ASIDLEN, is 9 for Sv32 or 16 for Sv39, Sv48, and Sv57