OvmfPkg: pull in TLS modules with -D TLS_ENABLE (also enabling HTTPS)

OvmfPkg: pull in TLS modules with -D TLS_ENABLE (also enabling HTTPS)

This commit introduces a new build option, TLS_ENABLE, to pull in the
TLS-related modules. If HTTP_BOOT_ENABLE and TLS_ENABLE are enabled at
the same time, the HTTP driver locates the TLS protocols automatically
and thus HTTPS is enabled.

To build OVMF with HTTP Boot:

$ ./build.sh -D HTTP_BOOT_ENABLE

To build OVMF with HTTPS Boot:

$ ./build.sh -D HTTP_BOOT_ENABLE -D TLS_ENABLE

Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Justen Jordan L <jordan.l.justen@intel.com>
Cc: Wu Jiaxin <jiaxin.wu@intel.com>
Cc: Long Qin <qin.long@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Gary Lin <glin@suse.com>
Reviewed-by: Wu Jiaxin <jiaxin.wu@intel.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>