msm: clock-samarium: Add measurement support for bimc_gpu

Msmsamarium has a new bimc_gpu clock. Users of that clock might want
to measure the clock in debugfs to confirm its rate.

Change-Id: Ia970d6a72243cdf74400b918583ac781b9e42e5a
Signed-off-by: Junjie Wu <junjiew@codeaurora.org>