xenctx: Add -m (--memory) <maddr> option to dump memory at maddr.

xenctx: Add -m (--memory) <maddr> option to dump memory at maddr.

Currently not supported on ARM.

New routine read_mem_word() will correctly read a word that crosses
a page boundary.  It will not fault if the 2nd page can not be
mapped.

Moved xenctx because guest_word_t is not defined where it was.

Here is an example:

Memory (address ffffffff803ddf90):
 ffffffff80048d19 0000000000200800 ffffffff803e7801 0000000000086800
 0000000000000000 ffffffff80430720 ffffffff803e722f 80008e000010019c
 00000000ffffffff 0000000000000000 0000000000000000 0000000000200000
 0000000000000000 0000000000000000 0000000000000000 00cf9b000000ffff
 00af9b000000ffff 00cf93000000ffff 00cffb000000ffff 00cff3000000ffff

Signed-off-by: Don Slutz <Don@CloudSwitch.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>