Replace some instances of pub with pub(crate)

The recent fixes to private dependencies exposed some cases in the UEFI
module where private dependencies are exposed in a public interface.
These do not need to be crate-public, so change them to `pub(crate)`.

Author: tgross35

std/src/sys/pal/uefi/process.rs

@@ -388,7 +388,7 @@ mod uefi_command_internal {
             }
         }
 
-        pub fn start_image(&mut self) -> io::Result<r_efi::efi::Status> {
+        pub(crate) fn start_image(&mut self) -> io::Result<r_efi::efi::Status> {
             self.update_st_crc32()?;
 
             // Use our system table instead of the default one

std/src/sys/pal/uefi/time.rs

@@ -84,7 +84,7 @@ pub(crate) mod system_time_internal {
 
     // This algorithm is based on the one described in the post
     // https://blog.reverberate.org/2020/05/12/optimizing-date-algorithms.html
-    pub const fn uefi_time_to_duration(t: r_efi::system::Time) -> Duration {
+    pub(crate) const fn uefi_time_to_duration(t: r_efi::system::Time) -> Duration {
         assert!(t.month <= 12);
         assert!(t.month != 0);