MdeModulePkg/HiiDB: Reorganize codes of exporting HII settings

MdeModulePkg/HiiDB: Reorganize codes of exporting HII settings

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1235

Function "HiiGetConfigurationSetting" may be called
when HiiDatabase contents have been updated.
And it is just to call function "HiiGetDatabaseInfo" to
get the contents in HiiDatabase and call function
"HiiGetConfigRespInfo" and get the configuration response
string form HII drivers.

So here we can remove function "HiiGetConfigurationSetting"
and make caller to call "HiiGetDatabaseInfo" and
"HiiGetConfigRespInfo" directly.

And thus it also can distinguish which code blocks are to
operate HiiDatabase contents and which code blocks are not.
Then it's easy to know which code blocks should be atomic
when updating HiiDatabase contents.

Cc: Liming Gao <liming.gao@intel.com>
Cc: Eric Dong <eric.dong@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Dandan Bi <dandan.bi@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>