kernel_loader: return entry point of loaded kernel
kernel_loader: return entry point of loaded kernel

BUG=b:234155022
TEST=cargo test -p kernel_loader

Change-Id: I807d42a1cc5e2a88006fa4acc5bc7b089d0406af
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/3673613
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Alexandre Courbot <301cd6a3ea50a894b4b51e385c5eb12b9a4ffc0c@chromium.org>
Reviewed-by: Anton Romanov <7c8c28e1283c1d87f2c3df4d6b5c74b6ae02bcd9@google.com>
Commit-Queue: Daniel Verkamp <72bc170b46ec491f7bdd4359a1c0bfed274de40c@chromium.org>

google/crosvm,google/crosvm,google/crosvm,google/crosvm