halapi: common: Change variable name for improving the readability

halapi: common: Change variable name for improving the readability

Change the variable name for improving the readability
because prior defined variable name is vague to pass
the correct meaning of version. So that change the name as following
in order to improve the readability and understanding.

[Chagned variable names]
- g_curr_hal_abi_version	-> g_platform_curr_abi_version
- current_version		-> platform_abi_version
- compat_version		-> backend_min_abi_version

Change-Id: I733b203a6c0fe058dedb6e9e26f832a0629ccc15
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>