powerpc/pseries/htmdump: Add htm status support to htmdump module

Support dumping status of Hardware Trace Macro (HTM) function
via debugfs interface. Under debugfs folder
"/sys/kernel/debug/powerpc/htmdump", add file "htmstatus".
The interface allows only read of this file which will present the
content of HTM status buffer from the hcall. The 16th offset of HTM
status buffer has value for the number of HTM entries in the status
buffer. Each nest htm status entry is 0x6 bytes, where as core HTM
status entry is 0x8 bytes. Calculate the number of bytes to read
based on this detail.

Signed-off-by: Athira Rajeev <atrajeev@linux.ibm.com>
Tested-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20250420180844.53128-5-atrajeev@linux.ibm.com