Add a function converting a 7 characters string to its UINT32 EISAID. The algorithm used to create the EISAID is described in the ACPI 6.4 specification, s19.3.4 "ASL Macros". Reviewed-by: Sami Mujawar <sami.mujawar@arm.com> Signed-off-by: Pierre Gondois <Pierre.Gondois@arm.com>