msm: kgsl: Remove context debugfs nodes when detaching it

Removing debugfs nodes requires the debugfs SRCU to be synchronized,
which cannot be done in an atomic context. Remove the kgsl context
debugfs nodes when the context is detached instead of destroyed,
which may be in an interrupt context as the context memory and other
resources are freed asynchronously.

Change-Id: Iae9a12e0b92812f07cc42063033202fa07e0ef85
Signed-off-by: Lynus Vaz <lvaz@codeaurora.org>