ShellPkg: acpiview: IORT: Refactor PMCG node mapping count validation

ShellPkg: acpiview: IORT: Refactor PMCG node mapping count validation

Move Performance Monitoring Counter Group (PMCG) node ID mapping count
validation from the core IORT acpiview parser logic to a dedicated
function. Now, the pointer to the validation function is passed to the
IortNodePmcgParser[] ACPI_PARSER array.

This check does not affect the flow of IORT parsing and is limited to
a single table field in scope, therefore, it is better to keep it away
from the code responsible for traversing the table.

Signed-off-by: Krzysztof Koch <krzysztof.koch@arm.com>
Reviewed-by: Sami Mujawar <sami.mujawar@arm.com>
Reviewed-by: Jaben Carsey <jaben.carsey@intel.com>
Reviewed-by: Zhichao Gao <zhichao.gao@intel.com>