msm: npu: Remove explicit usage of __iormb()

Explicit usage of the __iormb() is not advisable, as the
implementation of this function is architecture specific,
which will result in build failures if the signature of
__iormb() changes on a particular architecture.

Thus, replace explicit usages of readl_relaxed(), followed by
__iormb() with the readl() wrappers, as this achieves the
same effect, while abstracting the internal implementation
of __iormb().

Change-Id: I2422d3b30f2a350c376b1c6a1245aa0d441020e0
Signed-off-by: Blagovest Kolenichev <bkolenichev@codeaurora.org>