SecurityPkg: SecureBootConfigDxe: Enhance secure boot string update logic

SecurityPkg: SecureBootConfigDxe: Enhance secure boot string update logic

ExtractConfig is called many times, so it's not efficient to update Secure Boot STR_SECURE_BOOT_STATE_CONTENT, STR_CUR_SECURE_BOOT_MODE_CONTENT string in ExtractConfig.
As these 2 strings are displayed on one form, always update them when opening the form.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Chao Zhang <chao.b.zhang@intel.com>
Reviewed-by: Fu Siyuan <siyuan.fu@intel.com>
Reviewed-by: Eric Dong <eric.dong@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@19645 6f19259b-4bc3-4df7-8a09-765794883524