dmi_scan: refactor dmi_scan_machine(), {smbios,dmi}_present()

dmi_scan: refactor dmi_scan_machine(), {smbios,dmi}_present()

Move the calls to memcpy_fromio() up into the loop in
dmi_scan_machine(), and move the signature checks back down into
dmi_decode().  We need to check at 16-byte intervals but keep a 32-byte
buffer for an SMBIOS entry, so shift the buffer after each iteration.

Merge smbios_present() into dmi_present(), so we look for an SMBIOS
signature at the beginning of the given buffer and then for a DMI
signature at an offset of 16 bytes.

[[email protected]: use proper buf type in dmi_present()]
Signed-off-by: Ben Hutchings <[email protected]>
Reported-by: Tim McGrath <[email protected]>
Tested-by: Tim Mcgrath <[email protected]>
Cc: Zhenzhong Duan <[email protected]>
Signed-off-by: Artem Savkov <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>