tifm_sd: separate command flags, socket flags and register bit masks

host->flags variable was hosting a collection of bits with different
semantics. For clarity, hardware bit masks are now defined as macros,
socket flags represented as bit fields and flags (now cmd_flags) only
hosts command processing modifiers.

Signed-off-by: Alex Dubov <oakad@yahoo.com>
Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>