ACPI: EC: Fix EC command visibility for dynamic debug

acpi_ec_cmd_string() currently is only enabled for "DEBUG" macro, but users
trend to use CONFIG_DYNAMIC_DEBUG and enable ec.c pr_debug() print-outs by
"dyndbg='file ec.c +p'". In this use case, all command names are turned
into UNDEF and the log is confusing. This affects bugzilla triage work.

This patch fixes this issue by enabling acpi_ec_cmd_string() for
CONFIG_DYNAMIC_DEBUG.

Tested-by: Wang Wendy <wendy.wang@intel.com>
Tested-by: Feng Chenzhou <chenzhoux.feng@intel.com>
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>