ARM: gic: rename gic_is_spi_pending and other API to generic name

Rename gic_is_spi_pending and gic_clear_spi_pending APIs
to generic gic_is_irq_pending and gic_clear_irq_pending names
since this API could be used for anyother interrupts, and while
at it also use proper style for the multi-line comments around
these APIs.

Change-Id: I7d440f3caa0ebc77483d1ba43eff7932d5ac6666
Signed-off-by: Trilok Soni <tsoni@codeaurora.org>