ACPI, APEI, Add APEI generic error status printing support

In APEI, Hardware error information reported by firmware to Linux
kernel is in the data structure of APEI generic error status (struct
acpi_hes_generic_status).  While now printk is used by Linux kernel to
report hardware error information to user space.

So, this patch adds printing support for the data structure, so that
the corresponding hardware error information can be reported to user
space via printk.

PCIe AER information printing is not implemented yet.  Will refactor the
original PCIe AER information printing code to avoid code duplicating.

The output format is as follow:

<error record> :=
APEI generic hardware error status
severity: <integer>, <severity string>
section: <integer>, severity: <integer>, <severity string>
flags: <integer>
<section flags strings>
fru_id: <uuid string>
fru_text: <string>
section_type: <section type string>
<section data>

<severity string>* := recoverable | fatal | corrected | info

<section flags strings>...