drivers: soc: qcom: Fix register names used with proper macros

Currently r0, r1, etc registers are used in scm driver.
To have compatibility between the arm and arm64 bit modes,
start using R0_STR, R1_STR, etc macros. GCC apparently lets
use r0, r1, etc. as register names even in arm64 mode but
clang does not. So by using marcos in inline assembly,
we can avoid compiler warnings.

Change-Id: I8a7103738bb6603693287afd22c0346cb397458e
Signed-off-by: Trilok Soni <tsoni@codeaurora.org>
Signed-off-by: Prasad Sodagudi <psodagud@codeaurora.org>
Signed-off-by: Shadab Naseem <snaseem@codeaurora.org>