drm: simplify device open
libdrm's open functions are just wrappers around open(), and our
detection of which parameter to pass to drmOpen() is not 100%
reliable.
Simplify the code and just call open() directly.
Bug: https://bugs.freedesktop.org/show_bug.cgi?id=71590
Origin: upstream, http://cgit.freedesktop.org/plymouth/commit/?id=
10e0810976722e746c2cdf1a77f5964703ee3387
Change-Id: If830eb866d1c37417a427ecc70d07acdf5def0f4
Signed-off-by: Krzysztof Sasiak <k.sasiak@samsung.com>