ShellPkg: Clarify the description of acpiview option '-s'

ShellPkg: Clarify the description of acpiview option '-s'

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=1153

The '-s' option of 'acpiview' do not support multiply invcation options.
So clarify it for users.
Modify the help decription for UefiShellAcpiViewCommandLib which the
description is equal or over 80 column. If the line include equal or over
80 characters. The display engine would display a blank line for those
equal 80 characters or a extra line with few words for those over 80
character. So it is better to keep each line less than 80 characters.

Cc: Jaben Carsey <jaben.carsey@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Signed-off-by: Zhichao Gao <zhichao.gao@intel.com>
Reviewed-by: Jaben Carsey <jaben.carsey@intel.com>