ShellPkg/UefiShellDebug1: Extract MainCmdXXX() function (1/4)

This patch aims to help breaking down the long functions present in
the ShellPkg and reduce complexity/nested code and conditions.

Extract a MainCmdXXX() function for each shell command.
This command contains the possible operations the command aims
to operate. The ShellCommandRunXXX() function from which it
is extracted is only responsible of:
- initializing the shell/command environment
- parsing the command parameter and creating a Package
- freeing the Package

For the MemMap and SetVar commands, ShellCommandLineFreeVarList()
calls are removed as the Package is now freed in the caller
function: ShellCommandRunXXX().

To avoid having one large commit updating all the UefiShellDebug1
commands, only update these files:
- Comp.c
- Cxl.c
- Dblk.c
- Dmem.c
- DmpStore.c

No functional change should be induced by this patch.

Signed-off-by: Pierre Gondois <pierre.gondois@arm.com>