Revert "Revert "Handle exceptions.""

This reverts commit 81334588b1ccc9ce36ee5b95d38950d5e4dbb8f2.

Reason for revert: Relanding original change with fix.

Bug: 223166344
Test: Ran unprotected VM under crosvm.
Change-Id: Ia1a73afef6df10a8fecec8321233b4d8855329be
diff --git a/pvmfw/entry.S b/pvmfw/entry.S
index e5c6045..f0021be 100644
--- a/pvmfw/entry.S
+++ b/pvmfw/entry.S
@@ -145,6 +145,10 @@
 	adr_l x30, boot_stack_end
 	mov sp, x30
 
+	/* Set up exception vector. */
+	adr x30, vector_table_el1
+	msr vbar_el1, x30
+
 	/* Call into Rust code. */
 	bl main