fix(lib/debug): Fix LOG_LEVEL for Multi-Config build

The CMAKE_BUILD_TYPE variable is invalid for Multi-Config builds.
The previous implementation depended on this to set the default
LOG_LEVEL for Debug and Release builds. This is now corrected to
an implementation which is compatible with Multi-Config build
generators.

fixes TF-RMM/tf-rmm#16

Signed-off-by: Soby Mathew <soby.mathew@arm.com>
Change-Id: I53a2d850b532ad169c09e0eeed4c485752be8a7a
diff --git a/docs/getting_started/build-options.rst b/docs/getting_started/build-options.rst
index 805482b..1907125 100644
--- a/docs/getting_started/build-options.rst
+++ b/docs/getting_started/build-options.rst
@@ -268,7 +268,7 @@
    MbedTLS_BUILD_TYPE		,Debug | Release	,Release		,"MbedTLS build type"
    RMM_PLATFORM			,fvp | host		,			,"Platform to build"
    RMM_TOOLCHAIN		,gnu | llvm		,			,"Toolchain name"
-   LOG_LEVEL			,			,40			,"Log level to apply for RMM (0 - 50)"
+   LOG_LEVEL			,0 - 50			,40(Debug) 20(Release)	,"Log level to apply for RMM (0 - 50)."
    RMM_STATIC_ANALYSIS		,			,			,"Enable static analysis checkers"
    RMM_UART_ADDR		,			,0x0			,"Base addr of UART to be used for RMM logs"
    PLAT_CMN_CTX_MAX_XLAT_TABLES ,			,0			,"Maximum number of translation tables used by the runtime context"