pc-bios: Add support for List-Directed IPL from ECKD DASD

pc-bios: Add support for List-Directed IPL from ECKD DASD

Check for a List Directed IPL Boot Record, which would supersede the CCW type
entries.  If the record is valid, proceed to use the new style pointers
and perform LD-IPL. Each block pointer is interpreted as either an LD-IPL
pointer or a legacy CCW pointer depending on the type of IPL initiated.

In either case CCW- or LD-IPL is transparent to the user and will boot the same
image regardless of which set of pointers is used. Because the interactive boot
menu is only written with the old style pointers, the menu will be disabled for
List Directed IPL from ECKD DASD.

If the LD-IPL fails, retry the IPL using the CCW type pointers.

If no LD-IPL boot record is found, simply perform CCW type IPL as usual.

Signed-off-by: Jared Rossi <jrossi@linux.ibm.com>
Message-Id: <20230221174548.1866861-2-jrossi@linux.ibm.com>
[thuth: Drop some superfluous parantheses]
Signed-off-by: Thomas Huth <thuth@redhat.com>