kvm-unit-tests: VMX: Add test cases for vmentry checks

This patch design a framwork to check vmentry fields, then test
all supported features in Intel SDM 26.1 and 26.2. Unsupported
features are not tested, but listed in the code.

To add new tests for vmentry checks, just write functions for
test initialization and add related item in vmentry_cases.

Signed-off-by: Arthur Chunqi Li <yzt356@gmail.com>