Previously request_{bios, pflash} cases were skipped on win32, mainly
due to create_blob_file() calling mmap() which does not exist on win32.
This rewirtes create_blob_file() to be portable, so that we can enable
these cases on Windows.

Suggested-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Bin Meng <bin.meng@windriver.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20220925113032.1949844-2-bmeng.cn@gmail.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>