lib/hwfeatures-gcry: Introduce functions to manage hardware features

lib/hwfeatures-gcry: Introduce functions to manage hardware features

This commit introduces the generic functions to manage the hardware
features in libgcrypt. These functions are stubs for future
platform-specific implementations:
  - grub_gcry_hwf_enabled() returns __gcry_use_hwf which indicates if
    the hardware features are enabled specifically by grub_enable_gcry_hwf(),
  - grub_enable_gcry_hwf() invokes the architecture specific enablement
    functions and sets __gcry_use_hwf to true,
  - grub_reset_gcry_hwf() invokes the architecture specific reset
    functions and sets __gcry_use_hwf to false.

Signed-off-by: Gary Lin <glin@suse.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>