vmbase: Temporarily disable logging in exception handlers

Add `logger::block` which temporarily disables logging. This should be used
to prevent log messages being sent to UART from exception handlers. It
allows calling external code in exception handlers which may produce log
messages. Also stop exporting `println` macros from vmbase for the same
reason and use log macros instead.

Bug: 245267332
Test: atest vmbase_example.integration_test

Change-Id: I99e5ea1fa15e7371fd680e4086a3685ac489111d
diff --git a/vmbase/example/src/layout.rs b/vmbase/example/src/layout.rs
index 4c3af6d..e660c5f 100644
--- a/vmbase/example/src/layout.rs
+++ b/vmbase/example/src/layout.rs
@@ -17,8 +17,8 @@
 use aarch64_paging::paging::{MemoryRegion, VirtualAddress};
 use core::arch::asm;
 use core::ops::Range;
+use log::info;
 use vmbase::layout;
-use vmbase::println;
 use vmbase::STACK_CHK_GUARD;
 
 /// The first 1 GiB of memory are used for MMIO.
@@ -74,14 +74,14 @@
 
 pub fn print_addresses() {
     let dtb = dtb_range();
-    println!("dtb:        {}..{} ({} bytes)", dtb.start, dtb.end, dtb.end - dtb.start);
+    info!("dtb:        {}..{} ({} bytes)", dtb.start, dtb.end, dtb.end - dtb.start);
     let text = text_range();
-    println!("text:       {}..{} ({} bytes)", text.start, text.end, text.end - text.start);
+    info!("text:       {}..{} ({} bytes)", text.start, text.end, text.end - text.start);
     let rodata = rodata_range();
-    println!("rodata:     {}..{} ({} bytes)", rodata.start, rodata.end, rodata.end - rodata.start);
-    println!("binary end: {}", binary_end());
+    info!("rodata:     {}..{} ({} bytes)", rodata.start, rodata.end, rodata.end - rodata.start);
+    info!("binary end: {}", binary_end());
     let data = data_range();
-    println!(
+    info!(
         "data:       {}..{} ({} bytes, loaded at {})",
         data.start,
         data.end,
@@ -89,9 +89,9 @@
         data_load_address(),
     );
     let bss = bss_range();
-    println!("bss:        {}..{} ({} bytes)", bss.start, bss.end, bss.end - bss.start);
+    info!("bss:        {}..{} ({} bytes)", bss.start, bss.end, bss.end - bss.start);
     let boot_stack = boot_stack_range();
-    println!(
+    info!(
         "boot_stack: {}..{} ({} bytes)",
         boot_stack.start,
         boot_stack.end,