Save the debug and error logs in mok-variables

[vathpela]

This changes our debug and error logging to save the entire logs into mok-variables as "shim-dbg.txt" and "shim-log.txt".

[vathpela]

The result here is you get something like:
[root@wdk23 ~]# hexdump -C /sys/firmware/efi/mok-variables/shim-dbg.txt | head 00000000 73 00 68 00 69 00 6d 00 2e 00 63 00 3a 00 31 00 |s.h.i.m...c.:.1.| 00000010 39 00 38 00 33 00 3a 00 65 00 66 00 69 00 5f 00 |9.8.3.:.e.f.i._.| 00000020 6d 00 61 00 69 00 6e 00 28 00 29 00 20 00 76 00 |m.a.i.n.(.). .v.| 00000030 65 00 6e 00 64 00 6f 00 72 00 5f 00 61 00 75 00 |e.n.d.o.r._.a.u.| 00000040 74 00 68 00 6f 00 72 00 69 00 7a 00 65 00 64 00 |t.h.o.r.i.z.e.d.| 00000050 3a 00 30 00 78 00 39 00 33 00 30 00 39 00 37 00 |:.0.x.9.3.0.9.7.| 00000060 30 00 31 00 30 00 20 00 76 00 65 00 6e 00 64 00 |0.1.0. .v.e.n.d.| 00000070 6f 00 72 00 5f 00 61 00 75 00 74 00 68 00 6f 00 |o.r._.a.u.t.h.o.| 00000080 72 00 69 00 7a 00 65 00 64 00 5f 00 73 00 69 00 |r.i.z.e.d._.s.i.| 00000090 7a 00 65 00 3a 00 30 00 0d 00 0a 00 00 00 73 00 |z.e.:.0.......s.| [root@wdk23 ~]#
which is far from perfect but pretty usable with something like:
[root@wdk23 ~]# iconv -f UCS2 -t UTF8 /sys/firmware/efi/mok-variables/shim-dbg.txt | tr -d '\0' | head shim.c:1983:efi_main() vendor_authorized:0x93097010 vendor_authorized_size:0 shim.c:1985:efi_main() vendor_deauthorized:0x93097010 vendor_deauthorized_size:0 sbat.c:492:set_sbat_uefi_variable() Default sbat policy: automatic sbat.c:553:set_sbat_uefi_variable() shim SBAT reparse before application sbat.c:339:parse_sbat_var() SBAT variable entries: sbat.c:344:parse_sbat_var() sbat, 1, 2021030218 pe.c:376:verify_sbat_section() SBAT section data

[jsetje]

I would change 4096 on line 149 of errlog.c to PAGE_SIZE, even if it will probably always be 4k. Otherwise this looks.