eal: add a new helper for wait until scheme

eal: add a new helper for wait until scheme

Add a new generic helper which is a macro for wait until scheme.

Furthermore, to prevent compilation warning in arm:
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'warning: implicit declaration of function ...'
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Delete 'undef' constructions for '__LOAD_EXC_xx', '__SEVL' and '__WFE'.
And add ‘__RTE_ARM’ for these macros to fix the namespace.
This is because original macros are undefine at the end of the file.
If the new macro calls them in other files, they will be seen as
'not defined'.

Signed-off-by: Feifei Wang <feifei.wang2@arm.com>
Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>
Acked-by: Jerin Jacob <jerinj@marvell.com>