libdrm: fix bad strncpy / snprintf calls

Fix the following bugs reported by IOActive:
* GOOGLE-AN01 - Android libdrm drm_parseDM.c Boundary-CRLF Buffer Overflow
* GOOGLE-AN02 - Android libdrm 'drm_parseDM.c' contentType-CRLF Buffer Overflow
* GOOGLE-AN03 - Android libdrm drm_parseDM.c contentID-CRLF Buffer Overflow
* GOOGLE-AN04 - Android libdrm 'parser_dcf.c' Multiple Headers Buffer Overflow
* GOOGLE-AN05 - Android libdrm 'parser_dcf.c' ContentType Buffer Overflow

Bug: 8727221

(cherry picked from commit 25619b2c)

Change-Id: I9a99c9b8a63c8b9efb3b2b650c735467b77120f2