efi: Rename memory allocation/free functions

efi: Rename memory allocation/free functions

Rename them to be more similar, as low_free() could be used to free
memory allocated by both high_alloc() and low_alloc().
high_alloc() -> efi_high_alloc()
low_alloc()  -> efi_low_alloc()
low_free()   -> efi_free()

Signed-off-by: Roy Franz <roy.franz@linaro.org>
Acked-by: Mark Salter <msalter@redhat.com>
Reviewed-by: Grant Likely <grant.likely@linaro.org>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>
(cherry picked from commit 40e4530a00b7d52332fe9a1361388fda8e5260da)
Signed-off-by: Mark Brown <broonie@linaro.org>