feat: add empty fn to all pte except aarch64

Author: yfblock

page_table_entry/src/arch/loongarch64.rs

@@ -125,6 +125,11 @@ pub struct LA64PTE(u64);
 
 impl LA64PTE {
     const PHYS_ADDR_MASK: u64 = 0x0000_ffff_ffff_f000; // bits 12..48
+
+    /// Creates an empty descriptor with all bits set to zero.
+    pub const fn empty() -> Self {
+        Self(0)
+    }
 }
 
 impl GenericPTE for LA64PTE {

page_table_entry/src/arch/riscv.rs

@@ -81,6 +81,11 @@ pub struct Rv64PTE(u64);
 
 impl Rv64PTE {
     const PHYS_ADDR_MASK: u64 = (1 << 54) - (1 << 10); // bits 10..54
+
+    /// Creates an empty descriptor with all bits set to zero.
+    pub const fn empty() -> Self {
+        Self(0)
+    }
 }
 
 impl GenericPTE for Rv64PTE {

page_table_entry/src/arch/x86_64.rs

@@ -58,6 +58,11 @@ pub struct X64PTE(u64);
 
 impl X64PTE {
     const PHYS_ADDR_MASK: u64 = 0x000f_ffff_ffff_f000; // bits 12..52
+
+    /// Creates an empty descriptor with all bits set to zero.
+    pub const fn empty() -> Self {
+        Self(0)
+    }
 }
 
 impl GenericPTE for X64PTE {