pvmfw: Resize stack region to 8 pages

Reduce the number of pages required (which seems to be 4-5 on a normal
boot) to reduce the work when mapping, unmapping, and clearing the
region.

Bug: 270684188
Test: atest MicrodroidHostTests
Change-Id: I626aea440b92c2462f7ca3c761fb66b51a596741
diff --git a/pvmfw/src/mmu.rs b/pvmfw/src/mmu.rs
index ee99710..c21b69b 100644
--- a/pvmfw/src/mmu.rs
+++ b/pvmfw/src/mmu.rs
@@ -47,7 +47,7 @@
 
 /// Region allocated for the stack.
 fn stack_range() -> Range<usize> {
-    const STACK_PAGES: usize = 40;
+    const STACK_PAGES: usize = 8;
 
     layout::stack_range(STACK_PAGES * PVMFW_PAGE_SIZE)
 }