Migrate llvm_asm! to asm!

The macro llvm_asm! finally got removed as 'asm!' got stabilized in
nightly. See
rust-lang/rust#70173 (comment)
and this gets shipped starting with nightly 2022-01-17.

According to
https://users.rust-lang.org/t/volatile-option-in-new-asm-macro/44289/2
assembly is volatile by default with asm!.

src/cpu.rs

@@ -20,9 +20,8 @@ pub fn core() -> u32 {
     let mut core = 0;
 
     #[cfg(any(esp32, esp32s3))]
-    #[allow(deprecated)]
     unsafe {
-        llvm_asm!("rsr.prid $0\nextui $0,$0,13,1" : "=r"(core) : : : "volatile");
+        asm!("rsr.prid {}\nextui {},{},13,1", out(reg) core);
     }
 
     core

src/lib.rs

@@ -1,4 +1,3 @@
-#![feature(llvm_asm)]
 #![cfg_attr(not(feature = "std"), no_std)]
 #![feature(generic_associated_types)] // For mutex
 

src/ulp/sys/cpu.rs

@@ -9,6 +9,7 @@ pub const ULP_RISCV_CYCLES_PER_US_DENUM: u32 = 10;
 pub const ULP_RISCV_CYCLES_PER_MS: u32 =
     ULP_RISCV_CYCLES_PER_US_NUM * (1000 / ULP_RISCV_CYCLES_PER_US_DENUM);
 
+use core::arch::asm;
 use crate::ulp::pac::*;
 use crate::ulp::reg::*;
 
@@ -17,9 +18,8 @@ pub fn get_ccount() -> u32 {
     #[allow(unused_assignments)]
     let mut ccount = 0;
 
-    #[allow(deprecated)]
     unsafe {
-        llvm_asm!("rdcycle $0" : "=r"(ccount) : : : "volatile");
+        asm!("rdcycle {}", out(reg) ccount);
     }
 
     ccount